I am sure that I do occasionally watch you tube through my browser. I don't know how many tabs would constitute too many, and when you say open, what do you mean? I am not doing anything different with this phone then any other Android that I have had over the last+/- decade.
The box that continuously pops up on my Android Note 3, with Verizon, refers to a "windows manager icon," and that I must close some windows and try again.....I have now 2 open pages, but that didn't do it. That was on advice from Verizon.