For those missing 'Virtual Reality Mode' under the view menu, this may help.

[Juandissimo]

I'm not sure if this will help anybody else, but I had a different skin running for Steam, which switched around some of the interface a bit. After trying to get virtual reality mode to appear under the view menu, I thought that maybe the skin was messing something up.

I switched the skin back to Steam default, restarted and then virtual reality mode had appeared. I also have -vrforce at the end of my shortcut, though I'm not sure if it was one or the other. When removing -vrforce, the vr mode menu stays.