You should try to get ahold of some more information about the blue screen. Is it a plain blue screen without any characters on it?
Anyway, you should take a look into C:\Windows\minidump directory, that's where the system crash logs go to die. Maybe there're a couple recent ones, with some error code we can Google around with. Which may also help finding out, if it's hardware or software, or combination.
(If nothing there, check this out:
http://forums.techguy.org/windows-vista/851183-bsod-error-log.html or this:
http://social.technet.microsoft.com/Forums/en-US/w7itprogeneral/thread/a5ebab26-61ef-42a4-a2bb-0fc60ad45385/ )
How come it's the browsers, and only the browsers... What do they have in common... networking? flash? graphics acceleration?
You reported back that Memtest was OK. Have you let it go around for several passes? (I'm looking for errors in the error-finding method now, crazy
)
You suspect it has something to do with the video cards. If you are comfortable opening up the case (precautions! static charge, etc.), have you thought of removing them and using the IntelHD for a while?