Since the latest Firefox update to 50.0 I had minor issues, occasional browser lock up, videos not playing on certain sites. This happened on all three of my machines, being as it was on all three I had to suspect the browser. I removed Firefox from all three today then did a fresh load on all three, now all work perfectly. If you are having similar issues follow my lead and get a fresh load, I have relied on updates only for may years without a hitch. None of the issues were in Internet Explorer!