All platforms with Firefox: Just uploaded a new version of the Better YouTube Firefox extension which now includes support for YouTube's high resolution videos. You already know that a simple URL hack can magically up the quality of some videos; now with Better YouTube installed, no URL modification's required. I highly recommend turning on YouTube HD with the Theater View in Better YouTube's options for quite the viewing experience. Grab the update from Firefox's Add-ons dialog, or click through to download it manually. Thanks to all the commenters for requesting this addition and to Yansky, YouTube Greasmonkey scripter extraordinaire, for the excellent user script.