The `gBrowser.reloadTab` method was doing a very light reload,
which could preserve iframe overriden locations.
The new method ensures we load the original HTML content back,
this seems to also have an impact on keep-alive which is not longer guaranteed.
Only supports reloading the currently selected tab, to better replicate
real user scenarios. But also to comply to `BrowserCommands.reload`,
which only supports reloading the selected tab.
Also tune the har test, now that requests are really cancelled
and we may try to fetch reponse content for such request.
Differential Revision: https://phabricator.services.mozilla.com/D277433
Alexandre Poirot
25c8ad77e8