I've updated Firefox and now some of the pages have got graphical glitch occurring in random moments. As for gmail I can't specify how to reproduce it, but on youtube it goes like this: 1. go to the random video 2. move the mouse cursor around (over the video and then over the title) 3. at one point the black background will show up under the videos in the right column or under the video timer

I've tried with and without acceleration with the same result (as attached).