Does this affect typical video sites like YouTube and Vimeo, or do you mean sites that have embedded videos from YouTube or Vimeo? Or other sites (in that case, please give examples)?

Hi jscher, thanks for your reply. Having checked it would seem it only happens with sites with mp4 videos, youtube appears to work ok. I had read on here that another user had the same issue and solved it with removing and re-installing, but that doesn't work for me. I recently added a codec pack, (Shark007), so will try removing that and see if anything changes.

Removed codec pack, issue still persists. I don't get the issue with internet explorer, just firefox.

Try to remove any other newly added add on. Check the settings of firefox where it decide what has to do with video playback when website is opened.!

Hi Woody420, thank you for the additional info.

Do you get blue checkmarks for at least the first five boxes on this test page:

https://www.youtube.com/html5

Do you use any add-ons related to videos? As a quick test to rule out an add-on issue, you could try the same sites in Firefox's Safe Mode. In its Safe Mode, Firefox temporarily deactivates extensions, hardware acceleration, and some other advanced features to help you assess whether these are causing the problem.

If Firefox is not running: Hold down the Shift key when starting Firefox. (On Mac, hold down the option/alt key instead of the Shift key.)

If Firefox is running: You can restart Firefox in Safe Mode using either:

• "3-bar" menu button > "?" Help button > Restart with Add-ons Disabled
• (menu bar) Help menu > Restart with Add-ons Disabled

and OK the restart.

Both scenarios: A small dialog should appear. Click "Start in Safe Mode" (not Refresh).

Any improvement?