Okay, here's a super-weird one.
If I compose a reply to this thread: http://chowhound.chow.com/topics/430267
... in the text editor, my left and right arrow keys don't seem to function. (Up and down function just fine.) No such problems on the rest of this site, nor any other site or any other application on my computer.
FireFox 23.0.1 running on Windows 7.