Recover from High Contrast Mode (Windows)
I'm currently using Firefox 76.0b7 and I noticed that Firefox seems do have problems when High Contrast Mode was enabled.
It's simple to reproduce: Windows-Key + L (Windows Lock Screen) At the right bottom corner enable switch on high contrast mode. Than switch off high contrast mode while still in lock screen. Logon again
My Firefox then shows only a blank window, altough it stills is responding. Actually my kid tends to mess with my computer while I'm AFK, this I how I noticed it.