I had Firefox 50.1.0 and when i tried to update to 51.0 i had to do it 2 times, because the first time failed when the browser restarted, and the same happened when i tried to update from 51.0 to 51.0.1, it was frustrating. When i was watching a video at FF 51.0 & 51.0.1 at YouTube, at fullscreen, i had the Firefox contextual menu opened and i pressed spacebar, so i saw a flash with the window controls (Minimize, Restore and Close) at the top of the screen, but they're from older version of Windows, (like Windows 95) style. The last is i see 2 Firefox on the Windows 10 programs installed list, and i have been having the same issue with Thunderbird. I see now Firefox 50.1.0 and Firefox 51.0.1 and Thunderbird 38.8.0 and Thunderbird 45.6.0 and i really don't understand why is happening this. I hope Mozilla can solve this and someone can explain me. Thank you so much and sorry for the inconveniences. Best regards.