YouTube – Disable HTML5 Video Player in Chrome

I'm not sure about Flash, but I recognize the problem you're having. Firefox's <video> support hasn't yet been done properly, so it's much slower than any other method.

If nobody else suggests something you like better, FlashVideoReplacer would let you swap out the YouTube-provided player for either the Quicktime or VLC plugin and both should run faster than Flash or Firefox's internal <video> support.

(It also supports various players which appear in their own windows, but you probably don't want that)

Another option you could try would be to track down WHY YouTube is forcing HTML5 on Firefox by trying these one-by-one:

• deleting all YouTube cookies (YouTube's fault but configurable)
• running in Safe Mode to disable extensions (One of your extensions' fault)
• using the User Agent Switcher extension (YouTube's fault, not intended to be configurable)

Finally, if none of that works, you could give Google Chrome a try. Its extension system isn't as powerful as Firefox's, but AdBlock Plus does have a version for it.

Okay I have done some research and found that this is a known issue and the Google team was able to reproduce the issue and is working on a fix. See Help Forum Article.

In case you don't want to wait for the fix to be implemented into the normal Google Chrome Build you can try Google Canary. Fixed it for me! Google Canary operates as a secondary browser, so you can have Google Chrome and Google Canary both installed and running at the same time it will not overwrite the old one like Google Chrome Beta does.

Edit: It's awesome to see the YouTube/Chrome team working to fix the issue! The issue has now been fixed according to another Answer they have made on the Help Forums. Crash Fixed Help Forum Link