If it is FF only problem (and not present w/ Chrome), have you tried installing a user-agent switcher extension, and pretend you are using Chrome? (To answer the question also: I'm an FF user, but only use Gmail web interface sporadically, and Youtube, also rarely. Both works fine nowadays.)
If it works in chrome but not Firefox it could be a profile issue with Firefox. Goto About:profiles in the address bar and create a new profile and see if the issue persists in the new profile. Mozilla forums would be a good place to check also.
If it works in chrome but not Firefox it could be a profile issue with Firefox. Goto About:profiles in the address bar and create a new profile and see if the issue persists in the new profile. Mozilla forums would be a good place to check also.
I have had issues with YouTube constantly buffering video for several months now, only on Firefox.