I have a pretty strange problem with YouTube: when I just go on YouTube and watch any video through Firefox, Chrome or Chromium (both with Flash and HTML5 players), it works perfectly.
BUT! When I log into my Google account and try watching any video while being logged in, it doesn’t play; it just shows me the “rolling wheel” icon on the screen (as if is loading).
I've done this test on a completely fresh system, without any changes, and on a system with some drivers installed. I had the same result on absolutely all distributions of Linux that I've tried (Ubuntu 10.04 LTS, 12.04 LTS, 13.04, Mint, Fedora, OpenSuse).
So, where could be the problem?