Hi, There's a Firefox theme on the addons site called Photon Colors, which I found helps a lot.

Go to https://addons.mozilla.org/firefox/addon/photon-colors/ and click on Install Theme.

Thank you for your help, that really makes it a lot better. This dark blue theme is much more pleasent for my eyes and matches at least the taskbar colour, but before the update my window colour was called "middle red" by microsoft. I guess i could take a screenshot and then try to get the exact colour. Is there anywhere an option in the config, where i can configure my colour really free?

To set your own colors freely, I think you would need to use the Firefox Color extension:

https://addons.mozilla.org/firefox/addon/firefox-color/

Someone should ask Mozilla whether they could set the title bar colour to the Windows 10 standard (they should use the colour setting in the Windows user preferences). It is not at all user-friendly to urge users to install an AddOn just to get the functionality that is default in all other software products.

I wonder why in Firefox 89 it was decided to 1) no longer follow the OS colour scheme, and 2) no longer differentiate in a clear way between active and inactive Firefox windows. None of the included themes do this. A loss for accessibility.

The standard "System theme" is supposed to "Follow the operating system setting for buttons, menus, and windows" yet it doesn't, it just shows a white titlebar for me, where the OS (Windows) uses another colour.

I use "Firefox Color" now. It doesn't let me follow the OS either, but I can use it to manually match Firefox to the OS, and to differentiate between active and inactive windows. Next time I change the colours in the OS, I'd have to manually change the Firefox colours again to match. Seems unnecessarily cumbersome.

Hi glye, jscher2000's post was marked as the solution by the person who asked the original question (billerus). Your issue may have similar symptoms, but it is likely a different cause/solution. For better help, it would be best to use https://support.mozilla.org/en-US/questions/new where volunteers can get more details about your setup.

Because this thread is solved and more people might start using it for their own questions, I'm going to lock it.