I recently updated my 2010 MacBook Pro all the way from Snow Leopard 10.6.8 to Mavericks 10.9.1.
Today, I updated Mavericks to 10.9.2 in order to fix the nasty Mac OS X SSL vulnerability. Sadly, after the update, when I tried to start Firefox, it would hang. I tried repeatedly, but I would get no window, no error, just a Firefox main menu with no File, Edit or other menus.
I did a lot of research but could find nothing that explained precisely this behavior.
I tried installing a second copy of Firefox. I tried deleting my original installation. I tried turning off my firewall. I tried deleting my profiles. I went through all kinds of machinations, but nothing worked. No matter how clean a start I seemed to give it, Firefox would (a) hang, and (b) fail to quit. I had to Force Quit every time.
Well, here’s the “funny” part of the story. After all that, I somehow ended up swiping to a second desktop on my Mac (by scrolling to the right with three fingers). And what was there? Firefox.
Coming from Snow Leopard, I’m a little fuzzy on exactly why, how, and when Desktops come into being and how apps get allocated to them. But, for whatever reason, Firefox acted for all the world as if it was hung, while it was actually just running on a different Desktop.