I have both a 2012 MBP retina and a 2012 MBP non-retina. Both are running Mountain Lion which I need to stay at for program compatibility. They both have developed the same problem recently and I can't figure out why. I shut them down and check the box "reopen windows in next session..." . Usually only firefox and textedit are open a that time. Later, when I start either of them, everything opens okay, except that the textedit files now open with black type on black background (basically a big black box). They were created and saved with black text on white background. If I highlight in the text field, the parts that I highlight switch back to a white background instantly. Part that I haven't highlighted remain black. Sometimes if I move the text edit window, it leaves behind a black box where it was at startup. The box goes away if I highlight or click more in the text edit windows. If I create a new textedit file, it opens fine and normal. Only the files that auto-open on startup are affected. It's definitely a graphic drawing issue, but its started out of nowhere. 2 different machines, one with a clean install, one with an older install, neither exhibiting a problem like this before. The only thing I can think of is that I started using Firefox on them somewhat recently and it is a program that also auto-starts in this scenario. But the problem didn't start right after installing Firefox, everything was fine for a few months until just the past 2 weeks. Does anyone have any ideas? I don't think it's mechanical (2 different machines), I don't think it's the OS (new install on one, old install on the other, nary a problem in the past). Could Firefox do something like this?