Is this with many websites, some, a few?

I see you do not have the flash player listed in your system details. Some sites are still using flash player.

This seems to be the most problematic with You Tube ....ie vids on HSN site etc.....but even vids from local news feeds will freeze up Firefox.....this just started a little over a week ago.....have made know known changes to my PC [Lenovo all in one desk], or to anything on my computer.....if I switch over to different browser [IE] all is fine.

Hi kydzwest, could you check YouTube's HTML5 support page here:

https://www.youtube.com/html5

What do you see?

In Firefox 63, it's common to have blue checkmarks for all 6 boxes. In earlier versions of Firefox the last box often had a red mark.

That last box could be the problem...

Firefox 63 enabled support for VP9, which is a codec created by Google. Several users have requested a way to hide this capability from YouTube so they can continue to use older codecs because VP9 is hard on their CPU.

Two possible workarounds:

(A) The h264ify add-on:

https://addons.mozilla.org/firefox/addon/h264ify/

That hides both VP9 and VP8 support, so sites serve H.264/MP4 video instead.

(B) VP9 hider user script:

I created a userscript based on the h264ify extension that is more targeted -- it blocks VP9 without blocking VP8. It tested out working in Tampermonkey and Violentmonkey, but not in Greasemonkey.

Step 1 is to get a "monkey" extension that lets you inject snippets of script into web pages:

• https://addons.mozilla.org/firefox/addon/tampermonkey/
• https://addons.mozilla.org/firefox/addon/violentmonkey/

Step 2 is to install the script from here:

https://greasyfork.org/en/scripts/373685-hide-vp9-support-from-youtube

All 6 boxes are blue checked.....I'm not very tech savvy so I don't understand some of the other parts of your info .....sorry.....could you explain in simpler fashion?....Thank You

I think the simplest thing I can suggest is to try the h264ify extension and see whether it makes any difference.

Could you tell me [step by step] how to do this?

Oh, it's an add-on. You go to this page on the Add-ons site and look for the "Add to Firefox" button:

https://addons.mozilla.org/firefox/addon/h264ify/