I've had this problem ever since I got my rMBP 15" in 2012 where I'll initially be able to watch a YouTube video in the largest player size after starting Safari, but if I open a new tab, close the window and reopen another one or do something similar, it will default back to the smaller viewing size until I quit Safari and restart it. I'm not changing the width of the Safari browser and the largest size continuously works on my iMac. I've attached pics to show what I'm talking about. Is there a fix for this? I've tried joining YouTube's HTML5 program, but that hasn't solved the problem. Any help is appreciated. Thanks. The "largest" size. The smaller, yet larger player from the options.