This problem started recently (I think with v 45.0 and still there in 45.0.1 and 45.0.2 but might be before, I cannot remember) and specifically with whatsapp web page (https://web.whatsapp.com/) and an html5 video from (https://www.hacking-lab.com/). For whatsapp, it shows an empty panel on the left which should show the users list, and after few seconds (maybe after it is done loading the list) turns into black (see attached picture). The list is there, and i can click on the items but I cannot see what I am clicking. However, if I click on one of the invisible items, the users' list appears and it loads the chat messages on the right panel but that turns black. Clicking here and there toggles the view and I can see the messages but then other clicks hide them again. The video plays with audio and black picture, pausing it shows the frame correctly. I tried disabling graphics hardware acceleration as seen in some bugs but didn't help. Youtube html5 videos works great with no issues. After playing around and inspecting the page elements I found the cause of the problem, "border-radius", both of them the "whatsapp div tag" and the "hacking-lab video tag" have a border-radius set with some value. Unchecking that or setting it to zero fixes the issue. Fedora Linux 23 (x64), KDE Plasma 5, FF 45.0.2