The 1080p option isn't shown because YouTube requires Media Source Extentions enabled (HTML5 DRM) for this. You -can- enable this under about:config (media.medi

The 1080p option isn't shown because YouTube requires Media Source Extentions enabled (HTML5 DRM) for this. You -can- enable this under about:config (media.mediasource.enabled) but it's still experimental for now. When I tried it, it did show the 1080p option, but then I had very mixed results from the blank video, no audio, or the higher resolution video not actually loading. This should also only apply if you have the HTML5 player enabled on YouTube, the Flash player should still show the 1080p option.