Bug 2039213 - Fix customizableui tests for enterprise build

[victhorlopez]

Description

Bugzilla: Bug-2039213

fixes:

In general tests fail with uncaught rejection: DocumentFragment.querySelector: '#' is not a valid selector, this is because the we have two html link elements in the pannel, and the CustomizableUI uses id's programatically. I moved those ones in browser.xhtml as other items are doing.

• browser_884402_customize_from_overflow.js uses the FxA button from the "overflowable" menu and tries to customize it, because our badge is not customizable (i.e non removable) and we do not have FxA button, I used another button
• browser_923857_customize_mode_event_wrapping_during_reset.js same as above, I just used email button
• browser_editcontrols_update.js the test does different things, the problem in here is the expectation that we reach the "overflow" state, our "enterprise badge" has usually no size on this tests, as such I gave it a fake logo, to have a "organic size" (instead of just setting some random width)
• The test browser_976792_insertNodeInWindow.js is fixed upstream (see dependencies)

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Dependencies / Related Issues

• Depends on: https://bugzilla.mozilla.org/show_bug.cgi?id=2041653
• https://phabricator.services.mozilla.com/D302990

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Screenshots

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Testing

• Added tests
• Manual testing performed
  See test pass

[victhorlopez]

the original conditional here, ok(customizableButton, buttonId + " was found"); was working because the first button that overflows is the fxa, the email button takes more time to overflow, and that shows the original check was racy...

[1rneh]

Thanks, some small nits and one blocker related to using SpecialPowers.pushPrefEnv when instrumenting user preferences in tests.