Sister's MacBook--system?

[silvarios]

Yep, Lion only. You should use a different browser other than Safari. Safari on 10.6 or even 10.7 is beyond lousy. Firefox, Chrome, Opera, etc.

[MartyStickle]

I love this forum. Great advice.

[RAMd®d]

"…missing plug-in"

This means she has Flash installed and it's out of date. Seems like there have been a couple of updates in the last month or so.

If she didn't have Flash installed, most YT videos would play via HTML5. For whatever reason, some are Flash only.

On my two latest machines, I have not and won't install Flash. On the few videos sites that need Flash, I do as AA suggested- activate the Develop menu in the Safari prefs- Develop > User Agent > Safari iPad iOS7.

That's only failed me once, on one site. The next day it worked fine, so I'm sure it was something at their end.

[MartyStickle]

Just heard from my sister and she upgraded to the latest flash and all is well now. And to think I'm still heading up I-81 and haven't even gotten there and it's done. Yeah.