You tube videos won't load?

I have Windows XP and the latest Firefox. You tube used to load just fine. Slow sometimes but it worked.

Now youtube videos only load if I use Chrome.

I know I did something in Firefox or something that made each site authorize me to let them play a video before the Flash would load.
I dont know how to turn that off or where I turned it on.

I reset to factory settings in Firefox and cleared caches and had a beer to calm down... didn't work much.

Ad blocker caused some problems for me I think so got rid of it when I used a laptop.