* Define a new pref browser.tabs.contextmenu.altstructure.enabled to allow opt-in to a reorganized tab context menu * Add menu layout data for current and alternate menu structures * Refactoring in GenAI.sys.mjs to allow creating a single menu item for Summarize vs. the sub-menu * New test and promote one of the openTabContextMenu implementations to head.js (and remove the duplicates) * Add the nimbus feature and variable in FeatureManifest.yaml * Add comments to a couple of context menu strings to clarify their use Differential Revision: https://phabricator.services.mozilla.com/D307151