It may be that Kernel32.dll (a library file that handles sub-routines - but don't worry about that!) is corrupt. You could always try re-installing it from the Windows CD.
Any other linked files could also be suspect - what version of Windows are you on? Could you run System Restore?
Sometimes with 'stack' overflows, the system can't cope if you're flicking between sites and pages, trying to download too much at once.
If you can give an idea as to your setup, and how you use the net, more of us may be able to help.
Cheers
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If you're not on the edge, then you're taking up too much space.