Actually, its been in Firefox for at least as long as Chrome has existed... I can't remember a Firefox build without it, but... it's been a while.

You are, of course, correct. I don't know what I was thinking. I haven't really used ff since switching to chrome, although I find I do need to boot it up to make the occasional flash application work. Also, webkit-based browsers have some wonky css handling. I guess my brain has some sort of cognitive bias where I unknowingly attribute everything that's awesome about Chrome to Chrome itself.

Also, Ctrl-Z in Opera also works, which makes perfect sense and is less for the user to learn, and is discoverable (in the sense, they can go to the standard Edit -> Undo menu which is more visible.) Although actually, Opera also has a visible basket of closed tabs on the right of the tab bar, which is even better.