Affected versions

• Firefox 87.0b7
• Firefox 88.0a1

Affected platforms

• Windows 7
• Ubuntu 20.04
• macOS 10.15.7

Steps to reproduce

1. Launch Firefox
2. Enter customize mode
3. Tick titlebar option
4. Get in fullscreen mode
5. Untick titlebar option
6. Exit fullscreen mode

Expected result

• The browsers window refreshes and title bar is deactivated

Actual result

• Title bar is still active even if the option for it is unchecked

Regression range

• I will see for a regression.

Additional notes

• The issue can be seen in the attachment

I can reproduce with mozregression --launch 78, and even 68, so this is clearly not a recent issue. There's also an easy workaround: tick the titlebar checkbox twice more after returning from full screen. Given that the STR are also a bit peculiar, this doesn't seem high priority to me.

Reproduced on Win10 as well with 89.0a1 (2021-03-23).

Regression range:

• last good: 2018-11-08;
• first bad: 2018-11-09;
• mozregression resulted Pushlog URL.