Just a quick post to let everyone know which of Firefox's suggested fixes worked for me. I always appreciate it when people post about a fix that worked for them. It makes searching the forums easier.
I tried all the fixes suggested on this page
related to Real Player. None of them worked for me, so I moved on to downgrading Flash 11.3.
Because I felt like I had experienced problems before this current release, I skipped 11.2.
I uninstalled Flash 11.3 with the uninstaller available here
. I then followed the instructions on the same page to install 10.3. Now youtube works!!
However, I'm a little annoyed because I only upgrade Flash when I try to play something and it tells me I need to update for that video to play. This will probably be school related and so I'll end up just switching to Chrome or Safari anyway.