Please try the following: *Disable the Firefox hardware acceleration ^{[https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems More Details]} *Disable the Adobe Flashplayer acceleration ^{[https://support.mozilla.org/en-US/kb/forum-response-disable-hardware-acceleration-flash More Details]} *Ensure that your computer's graphic card is capable of play videos Can you play videos installed locally of your computer?