Please try : https://support.mozilla.org/en-US/kb/fix-common-audio-and-video-issues and https://support.mozilla.org/en-US/kb/fix-video-audio-problems-firefox-windows 1 more https://support.mozilla.org/en-US/kb/html5-audio-and-video-firefox

Your Flash is out of date, new version released 6 days ago https://get.adobe.com/flashplayer/otherversions/ Step 1: Select Operating System Step 2: Select A Version (Firefox, Win IE . . . .) Note: Other software is offered in the download. <Windows Only>

Please let us know if this solved your issue or if need further assistance.

Hello

I have done what you suggested.

I have also updated Flash, shockwave and my graphic card drivers.

Videos still freeze when running on HD quality in full screen but keep playing when I set a lower quality in full screen.

I think we can chalk that up to this being an old computer giving its maximum. Still it works a lot better than before.

Thank you for your help

Welcome

A new version of Flash is out Version: 27.0.0.170

Yup I would possibly say your pushing it. Might want move to the Extended Release Version : https://www.mozilla.org/en-US/firefox/organizations/

Please let us know if this solved your issue or if need further assistance.