So, Mr Oniya was surfing some adult sites today, and tried navigating away from one in particular after he was finished with it. Note, I said tried. I'm sure that you've all seen the sneaky pop-ups that say 'Are you sure you don't want to stay? Click "OK" to stay on this page, or "Cancel" to navigate away.' This one had the same text, but the window extended to the point where it went below the bottom of the monitor, even on the highest resolution. After switching the monitor's display to 'Portrait' (essentially flipping it on its side), I found that not only was the window excessively long, but there were no buttons!
The only way to get out of it was to kill the Firefox process (Ctrl-Alt-Del), and restart the computer - twice. The first time, Firefox respawned the tabs (like normal) and the second time, it apologized for not being able to respawn one of the tabs.
Thought people should know.