We want to stop forcing the aqua appearance, once we've fixed all the problems.

At the moment, it's a bit tricky to check for the problems that occur once we start respecting the system appearance. There may be a way to do it via a "defaults write" command on the command line, but the way I've been doing it is to make a local build with the changes to the Info.plist files.

It would be better if we could have a pref for this. For example widget.respect-system-appearance.

This patch also sets the Info.plist keys to <false/>, i.e. "we don't require aqua".

Depends on D51462

We have four instances of NSRequiresAquaSystemAppearance <true/> in the tree; this fixes two out of four:

• The parent process is now protected by the widget.macos.require-system-appearance pref.
• The updater never shows any UI, and if it does, it's probably using native controls which correctly adapt to Dark Mode.
• We cannot yet flip the switch for content processes (ipc/app/macbuild/Contents/Info.plist.in) as long as we still allow using the native theme in content processes, due to bug 1688113.
• And the crash reporter is tracked in bug 1697991.

Depends on D107749

https://hg.mozilla.org/mozilla-central/rev/60794002f3ef
https://hg.mozilla.org/mozilla-central/rev/ebf64c2e7256