Wow... I went out to do chores and when I came back I was in a thread and used my mouse wheel to scroll down the conversation. But as I did the font became smaller and smaller until it was so small I could no longer read it.
It took me a minute or so before I realized my mouse wheel was doing it.
I opened a new window and had the same problem.

Then I picked up my keyboard from the ground beside me and the problem stopped. A bag was barely touching the keyboard (the only icons there are "home", "email", "calculator", "Pause/break".

What the heck happened? Thankfully everything is back to normal now, but I don't want to have a repeat occurrence lol.