Windows taskbar won't pop up over Mozilla

Disable any graphics overlays like Nvidia's FPS counter.

There is no such on

Terminate as much background software as you can.

Go to about:third-party and try disabling third-party modules.

These are. Which one can be a problem?

I would start with disabling the Stardock ObjectDock module. You could also try disabling or uninstalling ObjectDock itself.

Hello!

I blocked each of them separately and did not improve.

Did you try uninstalling ObjectDock?

This error was already before the Objectdock was installed.

Yes and no. In the past, there were many similar problems Firefox browser, but the bug fixing tips were good at the time. Currently those repair tips didn't help me.