I've had this bug for several versons now, but currently in version 54: To Reproduce: 1. Go to a YouTube video that uses the HTML5 player. Sound and video should play. 2. Plug in or unplug a pair of headphones. Playback will stop, getting stuck. 3. Once this has occurred, the browser will get stuck trying to play ANY HTML5 video. Expected behavior is that media continues to play after headphones insertion/removal. Restarting the browser fixes the problem for now. This bug appears to be similar to Bug 1355520, but still occurs for me even though that bug was supposedly fixed two versions ago. I'm on Firefox 54.0b11, OS X 10.9.5.
Correction - 54.0b14.
This works again for me as of FF55.