Steps to reproduce: 1. Open a YouTube video, such as this one https://www.youtube.com/watch?v=jNQXAC9IVRw 2. Click one of the media buttons e.g. "Play" 3. Minimize the window 4. Restore the window 5. Notice that the entire Firefox window is now completely white and unresponsive. If you wait a few minutes it complains about the plugin-container crashing, though I usually kill it from the task manager to save time What is expected: The Firefox window to restore normally I have tried: - Restarting Firefox in safe-mode - Resetting my preferences - Resetting Firefox and none of these fix the problem. I don't know if this is an issue with Adobe Flash Player because it only happens on YouTube. Here is a GIF I recorded describing the issue (it doesn't fix itself, that's just the gif looping): http://i.imgur.com/gmR2Tt7.gif