I would advise not to go back to Firefox 6 but to solve the problem you are confronted with. Did you try to start Firefox with disabled add-ons? Maybe you have installed an add-on that causes this problem.

Go to Help > Restart with Add-ons Disabled… and try if Firefox 7 works.

If you work since years with Firefox and/or have installed lots of add-ons, I can also recommend creating a very fresh install: http://blog.mozilla.com/verdi/80/fix-firefox-windows-easy/ But attention: If you decide to do so, your bookmarks, passwords, ... will be removed! You could save them using Firefox Sync.

gion-andri, Stock answers that don't even reply to the question asked are of little help.

I have NO add-ons installed and have the same youtube problem.

How do I REVERT to Firefox 6?

Can it be done as easily as updating (and thereby breaking) Firefox was done?

Sorry cwaugh, if I couldn't convince you with my answer.

But downgrading to Firefox 6 would be really a security issue! Firefox 6 isn't maintaind anymore by Mozilla.

So let me try to help you getting Firefox 7 working. Are you, like drewcom823, also working on Mac OS X 10.5? Do you know if you are running into problems with the Flash or the HTML5 version of youtube? Are you using the latest version of Flash (https://www.mozilla.org/plugincheck/ )? And could you maybe describe a little more the problem you are running into on youtube? Does the page not load? Or only the video? Is an error displayed?

I don't know if a downgrade will work. When upgrading Firefox, some data (like maybe bookmarks or passwords) will be stored in a new form. I can't promise that Firefox 6 still can read all the data from Firefox 7. So I can't help you if you really want do downgrade, Sorry!

I would also like to know how to roll back to Firefox 6 from Firefox 7. A number of addons I use with great frequency no longer work. I do not want you to help me get Firefox 7 working. I do not care about the potential security issues. If you have the information I seek, I implore you to relinquish it.