You tube use to work fine for me in Fire Fox ...Now wont...I dont recall changing anything.
You tube just shows black screen, works fine in internet explorer.
Haven't upgraded or changed versions of firefox or added any plug=ins Im awarer of. Had several automatic updates come through of other programs, such as flash, ect. But I have refused to upgrade firefox due to having to give up screen grab which I love too much to do it, so have stayed with older version.