User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:99.0) Gecko/20100101 Firefox/99.0

Steps to reproduce:

• I'm using Ubuntu 21.10, and I have one monitor to 100% scale and another to 200% scale, as described in bug #1765020. I'm not sure whether this is also relevant to this bug.

• I created a new profile to test this. Screenshot 1 is the default appearance, when I have not changed layout.css.devPixelsPerPx yet.

• In about:config, change layout.css.devPixelsPerPx to 2.0. This works as expected for the time being (screenshot 2).

• After restarting Firefox, most of the UI is still at 2× scale, but certain UI
  text, such as in tab titles and right-click menus, is at 1× (screenshot 3).

• Changing layout.css.devPixelsPerPx back to the default of -1.0 while this tiny text state is active results in the tiny text scaling down too, until Firefox is restarted again (screenshot 4).

Actual results:

Certain UI text acts strangely, as described above

Expected results:

The appearance in screenshot 2 is correct; it should still look like this after restarting Firefox.

Changing layout.css.devPixelsPerPx back to the default of -1.0 while this tiny text state is active results in the tiny text scaling down too, until Firefox is restarted again (screenshot 4).

I just realized my wording here was unclear -- I did not restart between screenshots 3 and 4. Restarting after screenshot 4 resets to the appearance in screenshot 1.

The Bugbug bot thinks this bug should belong to the 'Core::Widget: Gtk' component, and is moving the bug to that component. Please correct in case you think the bot is wrong.

Just wanted to report that, although #1765020 still isn't working, this one does seem to have been fixed when I updated to 103.

Yes, this was fixed by bug 1773823