You probably don't have flash installed, and Firefox doesn't have Media Source Extension support for h264 yet, which YouTube has required for 480 and 1080 video

You probably don't have flash installed, and Firefox doesn't have Media Source Extension support for h264 yet, which YouTube has required for 480 and 1080 video since last October (IIRC). According to this bug, support for MSE h264 will be landing in Firefox 33. https://bugzilla.mozilla.org/show_bug.cgi?id=1027875 https://bugzilla.mozilla.org/show_bug.cgi?id=1027875