So what sites are we talking about? Your giving use vague specs to go on without any sites to verify what your talking about.

YouTube. There's some blur on fast movement.

Thanks for replying. I appreciate it.

Hi Yaron, if you right-click the video and then click "Stats for nerds" YouTube will show you quality stats for the video, including resolution, codec, and frame rate. Any surprises there?

Hello jscher2000,

In FF 52 the codecs used is "avc1" whereas in FF 64 it's "vp09". Interesting.

Thanks for your help. Appreciated.

Hi Yaron, the VP9 codec is very processor intensive in Firefox. You can hide Firefox's ability to process that codec from the site using this extension:

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

Any improvement?

Hello jscher2000,

Thanks again. I do appreciate your help.

Interestingly, disabling VP9 in about:config does not seem to have any effect.

The addon you have suggested indeed disables VP9 but, unfortunately, it does not resolve the issue.

Any other possibilities?

I checked a youtube fallout 76 walkthrough and it has VP9 and have no issues watching it. So since we have no link to which video your talking about to verify this sounds more like a System hardware video issue not a browser related.

Hello WestEnd,

Thanks again. Appreciated.

Well, I'll have to live with that. :)