Comment 1 for bug 55739

I've got what I think is the same problem, as mentioned at
http://ubuntuforums.org/showthread.php?t=255898
The pointer is movable, but it can't be used to click in anything, so you are usually stuck with having to restart X. On one occasion I managed to cure it by logging in via a remote terminal and killing Firefox (the application I clicked in which appeared to provoke the problem).

For me it is usually happens when using Firefox, but I believe I've seen it with another application, so I don't think it is Firefox's fault (though it's hard to be sure either way).

I'm also wondering if the bug reported at
https://launchpad.net/distros/ubuntu/+bug/52380
is the same thing.