I don't even know how this caused so many problems. Perhaps it's because of my niche operating environment, but I doubt it.

First off, the cursor was still movable, but it was impossible to window the fullscreened window. I decided to switch to TTY2 to attempt to terminate Firefox, as that helped unfreeze the game all other times, but typing ps -e lead to no firefox process turning up.

However, I did notice a process labeled "Web Content", so I tried terminating that. But that just lead to a defunct process, so I ps -ejH}}ed to get a process tree, and I noticed that {{java had started a xdg-open process which was controlling the now-defunct Web Content. So I tried terminating that. However, that still didn't unfreeze the game.

So I decided to just terminate the java process, and as expected, I got a "Game crashed!" message in the launcher. I then opened Firefox to attempt to report the bug, but when I did, the content area was white, and the back, forward, and refresh buttons were nonexistent. Attempting to type in a URL failed, and I had no idea how to fix this, so I just rebooted, and that fixed it.

I'm not sure how much of this is who's fault, honestly, but I figure that all the details is better than none.