From a2ae8bedb33cbab69a4dff4afd39c2b2c0009638 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Florian=20Qu=C3=A8ze?= <florian@queze.net>
Date: Sat, 5 Sep 2026 06:07:44 +0000
Subject: [PATCH] Bug 2069345 - Remove test.wait300msAfterTabSwitch from tests
 fixed by waiting for the tab to be reflowed. r=firefox-desktop-core-reviewers
 ,search-reviewers,tabbrowser-reviewers,layout-reviewers,nsharpley,dshin,scunnane,Gijs

Depends on D323604

Differential Revision: https://phabricator.services.mozilla.com/D323605
---
 .../content/test/contextMenu/browser_contextmenu_inspect.js | 6 ------
 .../test/contextMenu/browser_contextmenu_save_blocked.js    | 6 ------
 .../content/test/contextMenu/browser_copy_canvas_image.js   | 6 ------
 .../content/test/contextMenu/browser_strip_on_share_link.js | 5 +----
 .../test/contextMenu/browser_strip_on_share_nested_link.js  | 5 +----
 browser/base/content/test/forms/browser_selectpopup.js      | 5 +----
 .../content/test/forms/browser_selectpopup_color_scheme.js  | 5 +----
 .../base/content/test/forms/browser_selectpopup_colors.js   | 5 +----
 .../test/forms/browser_selectpopup_display_inherit.js       | 6 ------
 .../base/content/test/forms/browser_selectpopup_focus.js    | 6 ------
 .../content/test/forms/browser_selectpopup_option_in_div.js | 5 +----
 .../content/test/forms/browser_selectpopup_searchfocus.js   | 5 +----
 .../test/forms/browser_selectpopup_text_transform.js        | 6 ------
 .../content/test/forms/browser_selectpopup_user_input.js    | 5 +----
 .../base/content/test/forms/browser_selectpopup_width.js    | 5 +----
 .../base/content/test/forms/browser_selectpopup_xhtml.js    | 6 ------
 browser/base/content/test/general/browser_bug710878.js      | 6 ------
 .../base/content/test/general/browser_contentAltClick.js    | 6 ------
 .../content/test/general/browser_middleMouse_noJSPaste.js   | 6 +-----
 .../base/content/test/general/browser_newwindow_focus.js    | 6 ------
 .../downloads/test/browser/browser_image_mimetype_issues.js | 6 ------
 .../browser/browser_policy_block_set_desktop_background.js  | 4 ----
 .../extensions/test/browser/browser_ext_user_events.js      | 6 ------
 .../genai/tests/browser/browser_chat_contextmenu.js         | 6 ------
 browser/components/genai/tests/browser/browser_chat_page.js | 6 ------
 .../places/tests/browser/browser_bookmark_remove_tags.js    | 4 ----
 .../test/browser/browser_roundedWindow_open_min_inner.js    | 6 ------
 .../screenshots/tests/browser/browser_keyboard_shortcuts.js | 5 +----
 .../screenshots/tests/browser/browser_keyboard_tests.js     | 1 -
 .../components/search/test/browser/browser_contextmenu.js   | 4 ----
 .../tabs/browser_e10s_about_page_triggeringprincipal.js     | 5 +----
 ...rowser_link_in_tab_title_and_url_prefilled_new_window.js | 6 ------
 .../test/browser/tabs/browser_new_tab_insert_position.js    | 6 ------
 .../test/browser/tabs/browser_tab_groups_keyboard_focus.js  | 5 +----
 .../test/browser/tabs/browser_window_open_modifiers.js      | 6 ------
 .../test/navigation/browser_test-content-chromeflags.js     | 5 +----
 dom/base/test/browser_form_validity_popup_submit.js         | 6 ------
 dom/base/test/browser_outline_refocus.js                    | 6 ------
 dom/events/test/browser_mouseout_notification_panel.js      | 1 -
 dom/tests/browser/browser_pointerlock_warning.js            | 6 ------
 .../tests/browser_onbeforeunload_only_after_interaction.js  | 6 ------
 .../base/tests/browser_select_popup_from_background_tab.js  | 4 ----
 .../places/tests/browser/browser_visituri_restriction.js    | 1 -
 .../printing/tests/browser_print_bcg_id_overflow.js         | 6 ------
 .../thumbnails/test/browser_thumbnails_capture.js           | 6 ------
 .../thumbnails/test/browser_thumbnails_capture_svg.js       | 6 ------
 .../components/viewsource/test/browser/browser_srcdoc.js    | 6 ------
 .../windowwatcher/test/browser_new_remote_window_flags.js   | 5 +----
 .../browser/browser_default_image_filename_redirect.js      | 6 ------
 .../modules/tests/browser/browser_toTopLevelWidgetRect.js   | 6 +-----
 .../tests/mochitest/browser_txt_download_save_as.js         | 1 -
 51 files changed, 16 insertions(+), 248 deletions(-)

diff --git a/browser/base/content/test/contextMenu/browser_contextmenu_inspect.js b/browser/base/content/test/contextMenu/browser_contextmenu_inspect.js
index dd5050575e93..94241e9e1f70 100644
--- a/browser/base/content/test/contextMenu/browser_contextmenu_inspect.js
+++ b/browser/base/content/test/contextMenu/browser_contextmenu_inspect.js
@@ -3,12 +3,6 @@
 
 "use strict";
 
-add_setup(async function () {
-  await SpecialPowers.pushPrefEnv({
-    set: [["test.wait300msAfterTabSwitch", true]],
-  });
-});
-
 /**
  * Check that we show the inspect item(s) as appropriate.
  */
diff --git a/browser/base/content/test/contextMenu/browser_contextmenu_save_blocked.js b/browser/base/content/test/contextMenu/browser_contextmenu_save_blocked.js
index b6a45e8efd43..0ad0e0d4313a 100644
--- a/browser/base/content/test/contextMenu/browser_contextmenu_save_blocked.js
+++ b/browser/base/content/test/contextMenu/browser_contextmenu_save_blocked.js
@@ -19,12 +19,6 @@ function mockPromptService() {
   return promptService;
 }
 
-add_setup(async function () {
-  await SpecialPowers.pushPrefEnv({
-    set: [["test.wait300msAfterTabSwitch", true]],
-  });
-});
-
 add_task(async function test_save_link_blocked_by_extension() {
   let ext = ExtensionTestUtils.loadExtension({
     manifest: {
diff --git a/browser/base/content/test/contextMenu/browser_copy_canvas_image.js b/browser/base/content/test/contextMenu/browser_copy_canvas_image.js
index ba5871fb8af3..b449e696e4a1 100644
--- a/browser/base/content/test/contextMenu/browser_copy_canvas_image.js
+++ b/browser/base/content/test/contextMenu/browser_copy_canvas_image.js
@@ -4,12 +4,6 @@
 
 "use strict";
 
-add_setup(async function () {
-  await SpecialPowers.pushPrefEnv({
-    set: [["test.wait300msAfterTabSwitch", true]],
-  });
-});
-
 // Adapted from widget/tests/file_test_clipboard_pngPreservesTransparency.js
 async function getPNGFromClipboard(clipboard) {
   let trans = Cc["@mozilla.org/widget/transferable;1"].createInstance(
diff --git a/browser/base/content/test/contextMenu/browser_strip_on_share_link.js b/browser/base/content/test/contextMenu/browser_strip_on_share_link.js
index c56b8bbb379b..f69bae90c12c 100644
--- a/browser/base/content/test/contextMenu/browser_strip_on_share_link.js
+++ b/browser/base/content/test/contextMenu/browser_strip_on_share_link.js
@@ -10,10 +10,7 @@ let url =
 
 add_setup(async function () {
   await SpecialPowers.pushPrefEnv({
-    set: [
-      ["test.wait300msAfterTabSwitch", true],
-      ["privacy.query_stripping.strip_list", "stripParam"],
-    ],
+    set: [["privacy.query_stripping.strip_list", "stripParam"]],
   });
 
   // Get the list service so we can wait for it to be fully initialized before running tests.
diff --git a/browser/base/content/test/contextMenu/browser_strip_on_share_nested_link.js b/browser/base/content/test/contextMenu/browser_strip_on_share_nested_link.js
index 83758a71d775..230be7e1e8ec 100644
--- a/browser/base/content/test/contextMenu/browser_strip_on_share_nested_link.js
+++ b/browser/base/content/test/contextMenu/browser_strip_on_share_nested_link.js
@@ -10,10 +10,7 @@ const TEST_URL =
 
 add_setup(async function () {
   await SpecialPowers.pushPrefEnv({
-    set: [
-      ["test.wait300msAfterTabSwitch", true],
-      ["privacy.query_stripping.strip_list", "stripParam"],
-    ],
+    set: [["privacy.query_stripping.strip_list", "stripParam"]],
   });
 
   // Get the list service so we can wait for it to be fully initialized before running tests.
diff --git a/browser/base/content/test/forms/browser_selectpopup.js b/browser/base/content/test/forms/browser_selectpopup.js
index 15510d569daf..6ff868b4eb01 100644
--- a/browser/base/content/test/forms/browser_selectpopup.js
+++ b/browser/base/content/test/forms/browser_selectpopup.js
@@ -288,10 +288,7 @@ async function doSelectTests(contentType, content) {
 
 add_setup(async function () {
   await SpecialPowers.pushPrefEnv({
-    set: [
-      ["test.wait300msAfterTabSwitch", true],
-      ["dom.forms.select.customstyling", true],
-    ],
+    set: [["dom.forms.select.customstyling", true]],
   });
 });
 
diff --git a/browser/base/content/test/forms/browser_selectpopup_color_scheme.js b/browser/base/content/test/forms/browser_selectpopup_color_scheme.js
index a09b43b99175..4d6feb9f1e32 100644
--- a/browser/base/content/test/forms/browser_selectpopup_color_scheme.js
+++ b/browser/base/content/test/forms/browser_selectpopup_color_scheme.js
@@ -15,10 +15,7 @@ const TESTS = [
 
 add_setup(async function () {
   await SpecialPowers.pushPrefEnv({
-    set: [
-      ["test.wait300msAfterTabSwitch", true],
-      ["dom.forms.select.customstyling", true],
-    ],
+    set: [["dom.forms.select.customstyling", true]],
   });
 });
 
diff --git a/browser/base/content/test/forms/browser_selectpopup_colors.js b/browser/base/content/test/forms/browser_selectpopup_colors.js
index 074ebeafbe1d..baea65cfffe2 100644
--- a/browser/base/content/test/forms/browser_selectpopup_colors.js
+++ b/browser/base/content/test/forms/browser_selectpopup_colors.js
@@ -475,10 +475,7 @@ let kDefaultSelectStyles = {};
 
 add_setup(async function () {
   await SpecialPowers.pushPrefEnv({
-    set: [
-      ["test.wait300msAfterTabSwitch", true],
-      ["dom.forms.select.customstyling", true],
-    ],
+    set: [["dom.forms.select.customstyling", true]],
   });
   kDefaultSelectStyles = await BrowserTestUtils.withNewTab(
     `data:text/html,<select>`,
diff --git a/browser/base/content/test/forms/browser_selectpopup_display_inherit.js b/browser/base/content/test/forms/browser_selectpopup_display_inherit.js
index bb60a50fd0c0..e1ff0080ffbd 100644
--- a/browser/base/content/test/forms/browser_selectpopup_display_inherit.js
+++ b/browser/base/content/test/forms/browser_selectpopup_display_inherit.js
@@ -6,12 +6,6 @@ const PAGE = `
 </select>
 `;
 
-add_setup(async function () {
-  await SpecialPowers.pushPrefEnv({
-    set: [["test.wait300msAfterTabSwitch", true]],
-  });
-});
-
 add_task(async function () {
   const url = "data:text/html," + encodeURI(PAGE);
   await BrowserTestUtils.withNewTab({ gBrowser, url }, async function () {
diff --git a/browser/base/content/test/forms/browser_selectpopup_focus.js b/browser/base/content/test/forms/browser_selectpopup_focus.js
index 0a663a3fb755..24ff947c505f 100644
--- a/browser/base/content/test/forms/browser_selectpopup_focus.js
+++ b/browser/base/content/test/forms/browser_selectpopup_focus.js
@@ -12,12 +12,6 @@ function tick() {
   );
 }
 
-add_setup(async function () {
-  await SpecialPowers.pushPrefEnv({
-    set: [["test.wait300msAfterTabSwitch", true]],
-  });
-});
-
 add_task(async function () {
   const url = "data:text/html," + encodeURI(PAGE);
   await BrowserTestUtils.withNewTab(
diff --git a/browser/base/content/test/forms/browser_selectpopup_option_in_div.js b/browser/base/content/test/forms/browser_selectpopup_option_in_div.js
index c6e927baa4c3..bee60a8e11e1 100644
--- a/browser/base/content/test/forms/browser_selectpopup_option_in_div.js
+++ b/browser/base/content/test/forms/browser_selectpopup_option_in_div.js
@@ -12,10 +12,7 @@ const PAGE_CONTENT = `
 // select is enabled, so the dropdown has to list every <option> either way.
 async function testOptionsInDiv(customizableSelect) {
   await SpecialPowers.pushPrefEnv({
-    set: [
-      ["test.wait300msAfterTabSwitch", true],
-      ["dom.select.customizable_select.enabled", customizableSelect],
-    ],
+    set: [["dom.select.customizable_select.enabled", customizableSelect]],
   });
 
   const pageUrl = "data:text/html," + encodeURIComponent(PAGE_CONTENT);
diff --git a/browser/base/content/test/forms/browser_selectpopup_searchfocus.js b/browser/base/content/test/forms/browser_selectpopup_searchfocus.js
index 2de489f15c6c..558bf8d505cc 100644
--- a/browser/base/content/test/forms/browser_selectpopup_searchfocus.js
+++ b/browser/base/content/test/forms/browser_selectpopup_searchfocus.js
@@ -8,10 +8,7 @@ SELECT +=
 
 add_setup(async function () {
   await SpecialPowers.pushPrefEnv({
-    set: [
-      ["test.wait300msAfterTabSwitch", true],
-      ["dom.forms.selectSearch", true],
-    ],
+    set: [["dom.forms.selectSearch", true]],
   });
 });
 
diff --git a/browser/base/content/test/forms/browser_selectpopup_text_transform.js b/browser/base/content/test/forms/browser_selectpopup_text_transform.js
index 959d20eb37dd..04da532ddc71 100644
--- a/browser/base/content/test/forms/browser_selectpopup_text_transform.js
+++ b/browser/base/content/test/forms/browser_selectpopup_text_transform.js
@@ -6,12 +6,6 @@ const PAGE = `
 </select>
 `;
 
-add_setup(async function () {
-  await SpecialPowers.pushPrefEnv({
-    set: [["test.wait300msAfterTabSwitch", true]],
-  });
-});
-
 add_task(async function () {
   await SpecialPowers.pushPrefEnv({
     set: [["dom.forms.select.customstyling", true]],
diff --git a/browser/base/content/test/forms/browser_selectpopup_user_input.js b/browser/base/content/test/forms/browser_selectpopup_user_input.js
index c7f7f8ec36cf..2ba7a2ebb2a3 100644
--- a/browser/base/content/test/forms/browser_selectpopup_user_input.js
+++ b/browser/base/content/test/forms/browser_selectpopup_user_input.js
@@ -71,10 +71,7 @@ async function testHandlingUserInputOnChange(aTriggerFn) {
 
 add_setup(async function () {
   await SpecialPowers.pushPrefEnv({
-    set: [
-      ["test.wait300msAfterTabSwitch", true],
-      ["widget.macos.allow-native-select", false],
-    ],
+    set: [["widget.macos.allow-native-select", false]],
   });
 });
 
diff --git a/browser/base/content/test/forms/browser_selectpopup_width.js b/browser/base/content/test/forms/browser_selectpopup_width.js
index 749e764ddad7..8d7b5797cd62 100644
--- a/browser/base/content/test/forms/browser_selectpopup_width.js
+++ b/browser/base/content/test/forms/browser_selectpopup_width.js
@@ -14,10 +14,7 @@ function tick() {
 
 add_setup(async function () {
   await SpecialPowers.pushPrefEnv({
-    set: [
-      ["test.wait300msAfterTabSwitch", true],
-      ["widget.macos.allow-native-select", false],
-    ],
+    set: [["widget.macos.allow-native-select", false]],
   });
 });
 
diff --git a/browser/base/content/test/forms/browser_selectpopup_xhtml.js b/browser/base/content/test/forms/browser_selectpopup_xhtml.js
index 5a52752ae18b..27597eb5acf9 100644
--- a/browser/base/content/test/forms/browser_selectpopup_xhtml.js
+++ b/browser/base/content/test/forms/browser_selectpopup_xhtml.js
@@ -14,12 +14,6 @@ const PAGE = `<?xml version="1.0"?>
 </html>
 `;
 
-add_setup(async function () {
-  await SpecialPowers.pushPrefEnv({
-    set: [["test.wait300msAfterTabSwitch", true]],
-  });
-});
-
 add_task(async function () {
   const url = "data:application/xhtml+xml," + encodeURI(PAGE);
   await BrowserTestUtils.withNewTab(
diff --git a/browser/base/content/test/general/browser_bug710878.js b/browser/base/content/test/general/browser_bug710878.js
index 00a2c0f5227b..a91f8f9a1edd 100644
--- a/browser/base/content/test/general/browser_bug710878.js
+++ b/browser/base/content/test/general/browser_bug710878.js
@@ -4,12 +4,6 @@
 const PAGE =
   "data:text/html;charset=utf-8,<a href='%23xxx'><span>word1 <span> word2 </span></span><span> word3</span></a>";
 
-add_setup(async function () {
-  await SpecialPowers.pushPrefEnv({
-    set: [["test.wait300msAfterTabSwitch", true]],
-  });
-});
-
 /**
  * Tests that we correctly compute the text for context menu
  * selection of some content.
diff --git a/browser/base/content/test/general/browser_contentAltClick.js b/browser/base/content/test/general/browser_contentAltClick.js
index e8427551c3d7..053b78e89d00 100644
--- a/browser/base/content/test/general/browser_contentAltClick.js
+++ b/browser/base/content/test/general/browser_contentAltClick.js
@@ -54,12 +54,6 @@ async function clean_up() {
   BrowserTestUtils.removeTab(gBrowser.selectedTab);
 }
 
-add_setup(async function () {
-  await SpecialPowers.pushPrefEnv({
-    set: [["test.wait300msAfterTabSwitch", true]],
-  });
-});
-
 add_task(async function test_alt_click() {
   await setup();
 
diff --git a/browser/base/content/test/general/browser_middleMouse_noJSPaste.js b/browser/base/content/test/general/browser_middleMouse_noJSPaste.js
index 5e0bfb9d83a0..f023b78909f9 100644
--- a/browser/base/content/test/general/browser_middleMouse_noJSPaste.js
+++ b/browser/base/content/test/general/browser_middleMouse_noJSPaste.js
@@ -5,11 +5,7 @@ const middleMousePastePref = "middlemouse.contentLoadURL";
 const autoScrollPref = "general.autoScroll";
 
 add_task(async function () {
-  await pushPrefs(
-    ["test.wait300msAfterTabSwitch", true],
-    [middleMousePastePref, true],
-    [autoScrollPref, false]
-  );
+  await pushPrefs([middleMousePastePref, true], [autoScrollPref, false]);
 
   let tab = await BrowserTestUtils.openNewForegroundTab(gBrowser);
 
diff --git a/browser/base/content/test/general/browser_newwindow_focus.js b/browser/base/content/test/general/browser_newwindow_focus.js
index ac3f8c975223..18014f205c0a 100644
--- a/browser/base/content/test/general/browser_newwindow_focus.js
+++ b/browser/base/content/test/general/browser_newwindow_focus.js
@@ -7,12 +7,6 @@
 
 const PAGE = `data:text/html,<a id="target" href="%23" onclick="window.open('http://www.example.com', '_blank', 'width=100,height=100');">Click me</a>`;
 
-add_setup(async function () {
-  await SpecialPowers.pushPrefEnv({
-    set: [["test.wait300msAfterTabSwitch", true]],
-  });
-});
-
 /**
  * Test that when a new window is opened from content, focus moves
  * to the initial browser in that window once the window has finished
diff --git a/browser/components/downloads/test/browser/browser_image_mimetype_issues.js b/browser/components/downloads/test/browser/browser_image_mimetype_issues.js
index ef8440f03b53..7cc4097632a1 100644
--- a/browser/components/downloads/test/browser/browser_image_mimetype_issues.js
+++ b/browser/components/downloads/test/browser/browser_image_mimetype_issues.js
@@ -18,12 +18,6 @@ MockFilePicker.init();
  * they are.
  */
 
-add_setup(async function () {
-  await SpecialPowers.pushPrefEnv({
-    set: [["test.wait300msAfterTabSwitch", true]],
-  });
-});
-
 /**
  * Test the above with the "save image as" context menu.
  */
diff --git a/browser/components/enterprisepolicies/tests/browser/browser_policy_block_set_desktop_background.js b/browser/components/enterprisepolicies/tests/browser/browser_policy_block_set_desktop_background.js
index ebb694e31b58..0a36fee5a8f8 100644
--- a/browser/components/enterprisepolicies/tests/browser/browser_policy_block_set_desktop_background.js
+++ b/browser/components/enterprisepolicies/tests/browser/browser_policy_block_set_desktop_background.js
@@ -3,10 +3,6 @@
 "use strict";
 
 add_setup(async function () {
-  await SpecialPowers.pushPrefEnv({
-    set: [["test.wait300msAfterTabSwitch", true]],
-  });
-
   await setupPolicyEngineWithJson({
     policies: {
       DisableSetDesktopBackground: true,
diff --git a/browser/components/extensions/test/browser/browser_ext_user_events.js b/browser/components/extensions/test/browser/browser_ext_user_events.js
index 5294694ca81c..4852ffd124da 100644
--- a/browser/components/extensions/test/browser/browser_ext_user_events.js
+++ b/browser/components/extensions/test/browser/browser_ext_user_events.js
@@ -1,11 +1,5 @@
 "use strict";
 
-add_setup(async function () {
-  await SpecialPowers.pushPrefEnv({
-    set: [["test.wait300msAfterTabSwitch", true]],
-  });
-});
-
 // Test that different types of events are all considered
 // "handling user input".
 add_task(async function testSources() {
diff --git a/browser/components/genai/tests/browser/browser_chat_contextmenu.js b/browser/components/genai/tests/browser/browser_chat_contextmenu.js
index 47c346265ae2..64cdc1fe4e47 100644
--- a/browser/components/genai/tests/browser/browser_chat_contextmenu.js
+++ b/browser/components/genai/tests/browser/browser_chat_contextmenu.js
@@ -28,12 +28,6 @@ async function waitMenuState(menu, shouldHide, description) {
   }, description);
 }
 
-add_setup(async function () {
-  await SpecialPowers.pushPrefEnv({
-    set: [["test.wait300msAfterTabSwitch", true]],
-  });
-});
-
 registerCleanupFunction(() => {
   Services.prefs.clearUserPref("browser.ml.chat.page.menuBadge");
 });
diff --git a/browser/components/genai/tests/browser/browser_chat_page.js b/browser/components/genai/tests/browser/browser_chat_page.js
index 595745688b0a..37ee263dd158 100644
--- a/browser/components/genai/tests/browser/browser_chat_page.js
+++ b/browser/components/genai/tests/browser/browser_chat_page.js
@@ -112,12 +112,6 @@ function assertContextMenuStubResult(stub) {
 // Schedule reset to the initial sidebar state after the test.
 SidebarTestUtils.restoreStateAtCleanup(window);
 
-add_setup(async function () {
-  await SpecialPowers.pushPrefEnv({
-    set: [["test.wait300msAfterTabSwitch", true]],
-  });
-});
-
 /**
  * Check page, tab, and tool context menu have summarize prompt
  */
diff --git a/browser/components/places/tests/browser/browser_bookmark_remove_tags.js b/browser/components/places/tests/browser/browser_bookmark_remove_tags.js
index 34ce286c080e..c547e8114635 100644
--- a/browser/components/places/tests/browser/browser_bookmark_remove_tags.js
+++ b/browser/components/places/tests/browser/browser_bookmark_remove_tags.js
@@ -9,10 +9,6 @@ const TEST_TAG = "tag";
 
 // Setup.
 add_setup(async function () {
-  await SpecialPowers.pushPrefEnv({
-    set: [["test.wait300msAfterTabSwitch", true]],
-  });
-
   let toolbar = document.getElementById("PersonalToolbar");
   let wasCollapsed = toolbar.collapsed;
 
diff --git a/browser/components/resistfingerprinting/test/browser/browser_roundedWindow_open_min_inner.js b/browser/components/resistfingerprinting/test/browser/browser_roundedWindow_open_min_inner.js
index eb67ee022e25..f016a560ba4e 100644
--- a/browser/components/resistfingerprinting/test/browser/browser_roundedWindow_open_min_inner.js
+++ b/browser/components/resistfingerprinting/test/browser/browser_roundedWindow_open_min_inner.js
@@ -4,12 +4,6 @@
  *   minimum values.
  */
 
-add_setup(async function () {
-  await SpecialPowers.pushPrefEnv({
-    set: [["test.wait300msAfterTabSwitch", true]],
-  });
-});
-
 OpenTest.run([
   {
     settingWidth: 199,
diff --git a/browser/components/screenshots/tests/browser/browser_keyboard_shortcuts.js b/browser/components/screenshots/tests/browser/browser_keyboard_shortcuts.js
index 0d63e3493e76..66ab25f1c6cc 100644
--- a/browser/components/screenshots/tests/browser/browser_keyboard_shortcuts.js
+++ b/browser/components/screenshots/tests/browser/browser_keyboard_shortcuts.js
@@ -5,10 +5,7 @@
 
 add_task(async function test_download_shortcut() {
   await SpecialPowers.pushPrefEnv({
-    set: [
-      ["test.wait300msAfterTabSwitch", true],
-      ["browser.download.useDownloadDir", true],
-    ],
+    set: [["browser.download.useDownloadDir", true]],
   });
 
   let publicDownloads = await Downloads.getList(Downloads.PUBLIC);
diff --git a/browser/components/screenshots/tests/browser/browser_keyboard_tests.js b/browser/components/screenshots/tests/browser/browser_keyboard_tests.js
index 0a7555cebd33..b3537273799e 100644
--- a/browser/components/screenshots/tests/browser/browser_keyboard_tests.js
+++ b/browser/components/screenshots/tests/browser/browser_keyboard_tests.js
@@ -185,7 +185,6 @@ add_setup(async function () {
   await IOUtils.makeDirectory(tmpDir);
   await SpecialPowers.pushPrefEnv({
     set: [
-      ["test.wait300msAfterTabSwitch", true],
       ["browser.download.start_downloads_in_tmp_dir", true],
       ["browser.helperApps.deleteTempFileOnExit", true],
       ["browser.download.folderList", 2],
diff --git a/browser/components/search/test/browser/browser_contextmenu.js b/browser/components/search/test/browser/browser_contextmenu.js
index c99563964b61..6bf037f1985d 100644
--- a/browser/components/search/test/browser/browser_contextmenu.js
+++ b/browser/components/search/test/browser/browser_contextmenu.js
@@ -38,10 +38,6 @@ let oldDefaultEngine;
 let oldDefaultPrivateEngine;
 
 add_setup(async function () {
-  await SpecialPowers.pushPrefEnv({
-    set: [["test.wait300msAfterTabSwitch", true]],
-  });
-
   await SearchService.init();
 
   for (let [name, search_url] of ENGINE_DATA) {
diff --git a/browser/components/tabbrowser/test/browser/tabs/browser_e10s_about_page_triggeringprincipal.js b/browser/components/tabbrowser/test/browser/tabs/browser_e10s_about_page_triggeringprincipal.js
index b5cc4daa9377..8fbee64db4b9 100644
--- a/browser/components/tabbrowser/test/browser/tabs/browser_e10s_about_page_triggeringprincipal.js
+++ b/browser/components/tabbrowser/test/browser/tabs/browser_e10s_about_page_triggeringprincipal.js
@@ -23,10 +23,7 @@ const kAboutPagesRegistered = Promise.all([
 add_task(async function test_principal_click() {
   await kAboutPagesRegistered;
   await SpecialPowers.pushPrefEnv({
-    set: [
-      ["test.wait300msAfterTabSwitch", true],
-      ["dom.security.skip_about_page_has_csp_assert", true],
-    ],
+    set: [["dom.security.skip_about_page_has_csp_assert", true]],
   });
   await BrowserTestUtils.withNewTab(
     "about:test-about-principal-parent",
diff --git a/browser/components/tabbrowser/test/browser/tabs/browser_link_in_tab_title_and_url_prefilled_new_window.js b/browser/components/tabbrowser/test/browser/tabs/browser_link_in_tab_title_and_url_prefilled_new_window.js
index 675efc7febe1..b3b182188f36 100644
--- a/browser/components/tabbrowser/test/browser/tabs/browser_link_in_tab_title_and_url_prefilled_new_window.js
+++ b/browser/components/tabbrowser/test/browser/tabs/browser_link_in_tab_title_and_url_prefilled_new_window.js
@@ -11,12 +11,6 @@ Services.scriptloader.loadSubScript(
   this
 );
 
-add_setup(async function () {
-  await SpecialPowers.pushPrefEnv({
-    set: [["test.wait300msAfterTabSwitch", true]],
-  });
-});
-
 add_task(async function normal_page__blank_target() {
   await doTestWithNewWindow({
     link: "wait-a-bit--blank-target",
diff --git a/browser/components/tabbrowser/test/browser/tabs/browser_new_tab_insert_position.js b/browser/components/tabbrowser/test/browser/tabs/browser_new_tab_insert_position.js
index 91f9a7a323e9..9f271b0a825c 100644
--- a/browser/components/tabbrowser/test/browser/tabs/browser_new_tab_insert_position.js
+++ b/browser/components/tabbrowser/test/browser/tabs/browser_new_tab_insert_position.js
@@ -422,12 +422,6 @@ async function doTest(
   await promiseBrowserStateRestored(oldState);
 }
 
-add_setup(async function () {
-  await SpecialPowers.pushPrefEnv({
-    set: [["test.wait300msAfterTabSwitch", true]],
-  });
-});
-
 add_task(async function test_settings_insertRelatedAfter() {
   // Firefox default settings.
   await doTest(true, false, false);
diff --git a/browser/components/tabbrowser/test/browser/tabs/browser_tab_groups_keyboard_focus.js b/browser/components/tabbrowser/test/browser/tabs/browser_tab_groups_keyboard_focus.js
index fc3b91db6ce7..1bbbfb589f88 100644
--- a/browser/components/tabbrowser/test/browser/tabs/browser_tab_groups_keyboard_focus.js
+++ b/browser/components/tabbrowser/test/browser/tabs/browser_tab_groups_keyboard_focus.js
@@ -2,10 +2,7 @@
 
 add_setup(() =>
   SpecialPowers.pushPrefEnv({
-    set: [
-      ["test.wait300msAfterTabSwitch", true],
-      ["browser.tabs.groups.enabled", true],
-    ],
+    set: [["browser.tabs.groups.enabled", true]],
   })
 );
 
diff --git a/browser/components/tabbrowser/test/browser/tabs/browser_window_open_modifiers.js b/browser/components/tabbrowser/test/browser/tabs/browser_window_open_modifiers.js
index b1b311e0128e..47bd1269ea8a 100644
--- a/browser/components/tabbrowser/test/browser/tabs/browser_window_open_modifiers.js
+++ b/browser/components/tabbrowser/test/browser/tabs/browser_window_open_modifiers.js
@@ -27,12 +27,6 @@ const middleShiftEvent = { button: 1, shiftKey: true };
 const middleMetaEvent = { button: 1, [metaKey]: true };
 const middleMetaShiftEvent = { button: 1, [metaKey]: true, shiftKey: true };
 
-add_setup(async function () {
-  await SpecialPowers.pushPrefEnv({
-    set: [["test.wait300msAfterTabSwitch", true]],
-  });
-});
-
 add_task(async function testMouse() {
   await BrowserTestUtils.withNewTab(TEST_URL, async function (browser) {
     const tests = [
diff --git a/docshell/test/navigation/browser_test-content-chromeflags.js b/docshell/test/navigation/browser_test-content-chromeflags.js
index fff97bc25cd3..ab1ae41c0c47 100644
--- a/docshell/test/navigation/browser_test-content-chromeflags.js
+++ b/docshell/test/navigation/browser_test-content-chromeflags.js
@@ -12,10 +12,7 @@ add_task(async function () {
   await new Promise(resolve => {
     SpecialPowers.pushPrefEnv(
       {
-        set: [
-          ["test.wait300msAfterTabSwitch", true],
-          ["browser.link.open_newwindow", 2],
-        ],
+        set: [["browser.link.open_newwindow", 2]],
       },
       resolve
     );
diff --git a/dom/base/test/browser_form_validity_popup_submit.js b/dom/base/test/browser_form_validity_popup_submit.js
index 232f5471f5f1..2cefbf9d98be 100644
--- a/dom/base/test/browser_form_validity_popup_submit.js
+++ b/dom/base/test/browser_form_validity_popup_submit.js
@@ -22,12 +22,6 @@ const HTML = `
   </form>
 `;
 
-add_setup(async function () {
-  await SpecialPowers.pushPrefEnv({
-    set: [["test.wait300msAfterTabSwitch", true]],
-  });
-});
-
 add_task(async function bug_1790128() {
   await BrowserTestUtils.withNewTab(
     {
diff --git a/dom/base/test/browser_outline_refocus.js b/dom/base/test/browser_outline_refocus.js
index 7ca11645e669..066c25de6342 100644
--- a/dom/base/test/browser_outline_refocus.js
+++ b/dom/base/test/browser_outline_refocus.js
@@ -37,12 +37,6 @@ async function test_browser_outline_refocus(
   });
 }
 
-add_setup(async function () {
-  await SpecialPowers.pushPrefEnv({
-    set: [["test.wait300msAfterTabSwitch", true]],
-  });
-});
-
 add_task(async function browser_outline_refocus_mouse() {
   await test_browser_outline_refocus(
     "Link shouldn't show outlines since it was originally focused by mouse",
diff --git a/dom/events/test/browser_mouseout_notification_panel.js b/dom/events/test/browser_mouseout_notification_panel.js
index a8d31670c421..0eb673250ca8 100644
--- a/dom/events/test/browser_mouseout_notification_panel.js
+++ b/dom/events/test/browser_mouseout_notification_panel.js
@@ -91,7 +91,6 @@ add_setup(async function init() {
 
   await SpecialPowers.pushPrefEnv({
     set: [
-      ["test.wait300msAfterTabSwitch", true],
       ["test.events.async.enabled", true],
       // This test aims to synthesize mousemove events at specific times, so
       // disable the automatically synthesized mousemove events during reflow.
diff --git a/dom/tests/browser/browser_pointerlock_warning.js b/dom/tests/browser/browser_pointerlock_warning.js
index 320abef8c440..7a94b279b782 100644
--- a/dom/tests/browser/browser_pointerlock_warning.js
+++ b/dom/tests/browser/browser_pointerlock_warning.js
@@ -34,12 +34,6 @@ async function waitForWarningState(aWarningElement, aExpectedState) {
   );
 }
 
-add_setup(async function () {
-  await SpecialPowers.pushPrefEnv({
-    set: [["test.wait300msAfterTabSwitch", true]],
-  });
-});
-
 // Make sure the pointerlock warning is shown and exited with the escape key
 add_task(async function show_pointerlock_warning_escape() {
   let urls = [TEST_URL, FRAME_TEST_URL];
diff --git a/layout/base/tests/browser_onbeforeunload_only_after_interaction.js b/layout/base/tests/browser_onbeforeunload_only_after_interaction.js
index 7685cc45bf58..797225281a87 100644
--- a/layout/base/tests/browser_onbeforeunload_only_after_interaction.js
+++ b/layout/base/tests/browser_onbeforeunload_only_after_interaction.js
@@ -22,12 +22,6 @@ const PAGE_URL =
   "data:text/html," +
   encodeURIComponent("<script>(" + pageScript.toSource() + ")();</script>");
 
-add_setup(async function () {
-  await SpecialPowers.pushPrefEnv({
-    set: [["test.wait300msAfterTabSwitch", true]],
-  });
-});
-
 add_task(async function doClick() {
   // The onbeforeunload dialog should appear.
   let dialogPromise = PromptTestUtils.waitForPrompt(null, {
diff --git a/layout/base/tests/browser_select_popup_from_background_tab.js b/layout/base/tests/browser_select_popup_from_background_tab.js
index d3939b118699..7c5cce5396d0 100644
--- a/layout/base/tests/browser_select_popup_from_background_tab.js
+++ b/layout/base/tests/browser_select_popup_from_background_tab.js
@@ -61,10 +61,6 @@ async function test_clicking_select_window_open(aIsPopup) {
 
 // The select dropdown is created lazily, so initial it first.
 add_setup(async function init_select_popup() {
-  await SpecialPowers.pushPrefEnv({
-    set: [["test.wait300msAfterTabSwitch", true]],
-  });
-
   await BrowserTestUtils.withNewTab(
     {
       gBrowser,
diff --git a/toolkit/components/places/tests/browser/browser_visituri_restriction.js b/toolkit/components/places/tests/browser/browser_visituri_restriction.js
index 3d55a5c3ea44..c8cf0101d629 100644
--- a/toolkit/components/places/tests/browser/browser_visituri_restriction.js
+++ b/toolkit/components/places/tests/browser/browser_visituri_restriction.js
@@ -14,7 +14,6 @@ const TEST_PAGE = `data:text/html,
 add_setup(async function () {
   await SpecialPowers.pushPrefEnv({
     set: [
-      ["test.wait300msAfterTabSwitch", true],
       // Enable restriction feature.
       ["places.history.floodingPrevention.enabled", true],
       // Restrict from the second visit.
diff --git a/toolkit/components/printing/tests/browser_print_bcg_id_overflow.js b/toolkit/components/printing/tests/browser_print_bcg_id_overflow.js
index 3959224c67f3..3053afe236f5 100644
--- a/toolkit/components/printing/tests/browser_print_bcg_id_overflow.js
+++ b/toolkit/components/printing/tests/browser_print_bcg_id_overflow.js
@@ -21,12 +21,6 @@ const OPEN_NOOPENER_WINDOW = `
   <a rel="noopener" target="_blank" href="${OPENED_URI}">Open the window</a>
 `;
 
-add_setup(async function () {
-  await SpecialPowers.pushPrefEnv({
-    set: [["test.wait300msAfterTabSwitch", true]],
-  });
-});
-
 add_task(async function test_bc_id_overflow() {
   is(document.querySelector(".printPreviewBrowser"), null);
 
diff --git a/toolkit/components/thumbnails/test/browser_thumbnails_capture.js b/toolkit/components/thumbnails/test/browser_thumbnails_capture.js
index a21331a25217..5c6f95a64c39 100644
--- a/toolkit/components/thumbnails/test/browser_thumbnails_capture.js
+++ b/toolkit/components/thumbnails/test/browser_thumbnails_capture.js
@@ -1,12 +1,6 @@
 /* Any copyright is dedicated to the Public Domain.
    http://creativecommons.org/publicdomain/zero/1.0/ */
 
-add_setup(async function () {
-  await SpecialPowers.pushPrefEnv({
-    set: [["test.wait300msAfterTabSwitch", true]],
-  });
-});
-
 /**
  * These tests ensure that capturing a sites's thumbnail, saving it and
  * retrieving it from the cache works.
diff --git a/toolkit/components/thumbnails/test/browser_thumbnails_capture_svg.js b/toolkit/components/thumbnails/test/browser_thumbnails_capture_svg.js
index aa843cfe0a64..2beb574a109a 100644
--- a/toolkit/components/thumbnails/test/browser_thumbnails_capture_svg.js
+++ b/toolkit/components/thumbnails/test/browser_thumbnails_capture_svg.js
@@ -14,12 +14,6 @@ function getSVGUrl(fill) {
   );
 }
 
-add_setup(async function () {
-  await SpecialPowers.pushPrefEnv({
-    set: [["test.wait300msAfterTabSwitch", true]],
-  });
-});
-
 add_task(async function test_capture_svg() {
   // Create a tab with a red background.
   await BrowserTestUtils.withNewTab(
diff --git a/toolkit/components/viewsource/test/browser/browser_srcdoc.js b/toolkit/components/viewsource/test/browser/browser_srcdoc.js
index bf4b0d62d1f1..fbb07dd0ad3b 100644
--- a/toolkit/components/viewsource/test/browser/browser_srcdoc.js
+++ b/toolkit/components/viewsource/test/browser/browser_srcdoc.js
@@ -5,12 +5,6 @@
 const frameSource = `<a href="about:mozilla">good</a>`;
 const source = `<html><iframe srcdoc='${frameSource}' id="f"></iframe></html>`;
 
-add_setup(async function () {
-  await SpecialPowers.pushPrefEnv({
-    set: [["test.wait300msAfterTabSwitch", true]],
-  });
-});
-
 add_task(async function () {
   let url = `data:text/html,${source}`;
   await BrowserTestUtils.withNewTab({ gBrowser, url }, checkFrameSource);
diff --git a/toolkit/components/windowwatcher/test/browser_new_remote_window_flags.js b/toolkit/components/windowwatcher/test/browser_new_remote_window_flags.js
index a4393eeb541f..ae2bdc41b36d 100644
--- a/toolkit/components/windowwatcher/test/browser_new_remote_window_flags.js
+++ b/toolkit/components/windowwatcher/test/browser_new_remote_window_flags.js
@@ -11,10 +11,7 @@ const SCRIPT_PAGE = `data:text/html,<script>window.open("about:blank", "_blank")
 // of a new tab.
 add_setup(async function () {
   await SpecialPowers.pushPrefEnv({
-    set: [
-      ["test.wait300msAfterTabSwitch", true],
-      ["browser.link.open_newwindow", 2],
-    ],
+    set: [["browser.link.open_newwindow", 2]],
   });
 });
 
diff --git a/toolkit/content/tests/browser/browser_default_image_filename_redirect.js b/toolkit/content/tests/browser/browser_default_image_filename_redirect.js
index b37d33ff6d2a..f73aa5e28a4c 100644
--- a/toolkit/content/tests/browser/browser_default_image_filename_redirect.js
+++ b/toolkit/content/tests/browser/browser_default_image_filename_redirect.js
@@ -6,12 +6,6 @@
  * doggy.png in file picker dialog.
  */
 
-add_setup(async function () {
-  await SpecialPowers.pushPrefEnv({
-    set: [["test.wait300msAfterTabSwitch", true]],
-  });
-});
-
 let MockFilePicker = SpecialPowers.MockFilePicker;
 MockFilePicker.init();
 add_task(async function () {
diff --git a/toolkit/modules/tests/browser/browser_toTopLevelWidgetRect.js b/toolkit/modules/tests/browser/browser_toTopLevelWidgetRect.js
index 02d58125ecdb..bd85c02f0a66 100644
--- a/toolkit/modules/tests/browser/browser_toTopLevelWidgetRect.js
+++ b/toolkit/modules/tests/browser/browser_toTopLevelWidgetRect.js
@@ -1,11 +1,7 @@
 /* Any copyright is dedicated to the Public Domain.
  * http://creativecommons.org/publicdomain/zero/1.0/ */
 
-add_task(async function () {
-  await SpecialPowers.pushPrefEnv({
-    set: [["test.wait300msAfterTabSwitch", true]],
-  });
-});
+add_task(async function () {});
 
 add_task(async function test_toTopLevelWidgetRect() {
   const tab = await BrowserTestUtils.openNewForegroundTab(
diff --git a/uriloader/exthandler/tests/mochitest/browser_txt_download_save_as.js b/uriloader/exthandler/tests/mochitest/browser_txt_download_save_as.js
index c1652d84adca..a0f9e6e7bba2 100644
--- a/uriloader/exthandler/tests/mochitest/browser_txt_download_save_as.js
+++ b/uriloader/exthandler/tests/mochitest/browser_txt_download_save_as.js
@@ -90,7 +90,6 @@ async function setupFilePicker() {
 add_setup(async function () {
   await SpecialPowers.pushPrefEnv({
     set: [
-      ["test.wait300msAfterTabSwitch", true],
       ["browser.download.always_ask_before_handling_new_types", false],
       ["browser.download.useDownloadDir", false],
     ],