Thanks for your time and patience pm-r.
Oh I am almost 100% sure that user error could be involved. LOL
I do know about the theater button you mentioned and I have tried that and that is not it, and it was doing it before and after downloading El Capitan. It's not that big of a deal, just an extra click when starting a video, just has my curiosity up thats all.
I'm getting a bit confused here…
Are you saying your youtube viewing is working in full screen mode, but you just have to make "an extra click when starting a video" — whatever that is.
I have to click the full screen icon to get full screen mode working so I guess I'm missing something, but then again I don't have a 5K iMac as if it should make any difference to get it to work.
Maybe that's a "feature" with the 5K iMacs and maybe there's some display option or some setting/pref you could use…???
Haven't used one but a long experienced Mac user friend seems to be having odd problems with his, something he thinks has to do with pixel-doubling or lack of as he calls it with some apps.
At least you seem to be able to view them as you wish, but with just some extra clicking it seems.
Any chance you have some browser extensions enabled messing things up????
OK, let me try this....
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