You can try another Linux system theme to see whether another theme works better.

You can try the Firefox version from the official Mozilla server if you currently use a version from the repositories of your Linux distribution.

Sadly, It didn't fix my problem. It looks ugly in pages with black/white background....

You can try another Linux system theme to see whether another theme works better. You can try the Firefox version from the official Mozilla server if you currently use a version from the repositories of your Linux distribution.

Are you running Gnome or KDE? Try downloading another copy of Firefox to a folder and run it from there to see if you have the same issue.

https://www.mozilla.org/en-US/firefox/all/#product-desktop-release

Not able to replicate the issue. see screenshots

Operating System: openSUSE Tumbleweed 20210817 KDE Plasma Version: 5.22.4 KDE Frameworks Version: 5.85.0 Qt Version: 5.15.2 Kernel Version: 5.13.8-1-default (64-bit) Graphics Platform: X11 Processors: 8 × Intel® Core™ i7-4810MQ CPU @ 2.80GHz Memory: 31.0 GiB of RAM Graphics Processor: Mesa DRI Intel® HD Graphics 4600

This could be a problem with WebRender or hardware acceleration in Firefox. You can try to disable WebRender to see whether this has effect.

You can try to disable WebRender by setting this pref to true on the the about:config page to see if that has effect.

• gfx.webrender.force-disabled = true

You can open the about:config page via the location/address bar. You can accept the warning and click "I accept the risk!" to continue.

• https://support.mozilla.org/en-US/kb/about-config-editor-firefox

Hi, I've finally solved my problem!

I was using the GNOME/GTK Application Style on KDE Plasma LINMOS-Blue-1.1, just changing by Default made the trick :)

HTH

Greets