The URL Hack. Add &fmt=18 to the end of a normal YouTube URL. If there's a high quality version available, that extra string will cause it to load. For eg:
http://www.youtube.com/watch?v=jqZIYsyFvmk [Normal Link]
http://www.youtube.com/watch?v=jqZIYsyFvmk&fmt=18 [Higher Quality]
Alternatively,
You don't need a URL hack or Firefox extension to force YouTube to send you videos in the highest quality that's available: in your Account settings, you can tell YouTube to default to the higher-res, better audio version of clips when they're available. Apparently YouTube automatically detects your connection speed and chooses which video to feed you by default, but if you're always on a fast connection, changing this setting will hook you up straight away.
Now enjoy your videos :)
http://www.youtube.com/watch?v=jqZIYsyFvmk [Normal Link]
http://www.youtube.com/watch?v=jqZIYsyFvmk&fmt=18 [Higher Quality]
Alternatively,
You don't need a URL hack or Firefox extension to force YouTube to send you videos in the highest quality that's available: in your Account settings, you can tell YouTube to default to the higher-res, better audio version of clips when they're available. Apparently YouTube automatically detects your connection speed and chooses which video to feed you by default, but if you're always on a fast connection, changing this setting will hook you up straight away.
Now enjoy your videos :)