2014520 - Title bar missing with custom userChrome.css

Status: UNCONFIRMED

(Firefox :: Untriaged, defect)

Description

[Kamil]

Attachment: ff.png

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:147.0) Gecko/20100101 Firefox/147.0

Steps to reproduce:

1. Use custom userChrome.css which brings tabs bar on bottom
2. Put it here (if chrome folder does not exist - create it): AppData\Roaming\Mozilla\Firefox\Profiles\<your_profile_name>\chrome
3. Open Firefox for first time after logging in after turning PC on and logging in to Windows or after Firefox has not been used for a longer time (30 min+?)
4. There is a change that Firefox will miss title bar with buttons to minimize/maximize/close.
5. Close Firefox (no processes in task manager) and open again or click 2x F11.
6. Works.

Actual results:

I know that this bug is known since v144-145, i.e. 2000464, 1996961 or 1993474 and it had been theoretically resolved.

However it still occurs on my Windows PC (W10 22H2, 19045.6456).

What is important, I use custom userChrome.css file from here which brings me tabs bar on bottom. When I disable (rename/delete) file then title bar work after longer. I also have 2 PC's others with W10 and W11 and this custom .css work on them flawlessly.

I had discussed this with the author of the add-on and he is unable to find the source of the problem.

Running "fresh" Firefox without any addons/themes (but with that userChrome.css file) do not help.

I tried to "kill" manually everything related with Firefox (services), but it didn't make bug appear again. Only restarting PC or longer inactivity of using causes bug to re-appear.

Expected results:

Title bar should always appear.