On my system, at least, Youtube offers the full range of resolution options in both Firefox and Chrome. That said, the 4K versions don't look notably better than standard 1080p, but then Youtube is notorious for bit-starving videos at higher resolutions.
In feature film restoration news, WB has temporarily pulled Full Metal Jacket from theatrical distribution pending an upcoming event described as a "film festival." The festival isn't named, but they did provide the dates: May 12th through the 23rd. So it looks like this will be the next Kubrick to get a 4K restoration and it'll be making its bow at Cannes.