Hello When I play videos (html5) in firefox, the windows opened in the background shine through. It's only visible while playing the video, it disappears when I pause. Its also only a firefox issue, no problem with chrome. See also the picture, where you can see a white rectangle in the video screen (discreet but still annoying). Switching off hardware acceleration doesn't help, nor does it work properly in safe mode, so no plugin issue. I already reinstalled firefox. I'm using ubuntu 18.04. Everything should be up to date and no problems elsewhere. I really would appreciate not to have to switch to chrome, because I really like firefox. Thanks a lot in advance for your help.