Yeah, windows should not be closing by themselves...hmmm..I wish there was a way for websites to reliably crash browser windows...I can think of a practical joke or two for some friends..hehe...er...they'd probably crash my browser first....hmmm.
I'm still thinking browser issues or 3rd party application running with or without your knowledge. I'd get a 3rd and 4th opinion (browser-wise) and go run Opera 8 and Netscape 7.2 (NS8 runs the Firefox and IE engines) just to see how they do it. I'd also look at cleaning off anything "privacy," "pop-up," "Internet Security," or similarly related programs that modify how a browser accepts javascript. Maybe go get Belarc Advisor or Everest and run a check to get a list of which programs are running/installed on your system. AdAware, Spybot S&D, and running an antivirus check are fun tips to try (so is FDISK which always works, but it's a little bit of work). And last...
put on some clothes! **ducks thrown objects from the male population of the planet**