YouTube Video Resolution Severely Restricted

Tommygunn

TS Booster
I came back on Monday, after a weekend away, only to find that my Firefox browser or YouTube no longer allows me the choice as to the resolution of video I wish to play.
For some reason it only offers me '360' or 'Auto' along with overly large graphics. I've seen mention of HTML 5, but I don't know about that sort of thing, and all I did was turn the computer on after a few days or so.

Any fixes?

Tom.