Quote Originally Posted by tsu2 View Post
Speculating, there might be a problem with the player running in your FF.
First, I've found relatively few videos on Youtube are compiled to run at 1600pixel resolution, verify the option is avaiable and running as such using your Youtube video control buttons.
You might also try other browsers besides FF to see if it's a FF specific problem.
Should already be the case, but try forcing HTML5 instead of Flash, or vice versa. You can do this by going to the Youtube HTML5 configuration page, and of course you will need a Flash plugin to play Flash

I only use the HTML5 player, not the Flash one. Might see about the rest later: FF is currently my main browser, as for the video controls I always select the highest setting (eg: 1080p @ 60fps).