Installed Chrome - same issue with resolution/fuzziness.
Can't understand why as YT using Firefox is fast and normal resolution/clarity of image - just can't suppress the ads.
Speed tests on the broadband are about 60 down and 9 up which is better than I'm guaranteed - PC is about 6 years old but that shouldn't be an issue, especially as Firefox is fine.
BTW - VLC sort of works but lots of buffering, to the point of not being usable.
Weird.