Browsers crashing - Norton attack

Hi there. It has been for two days that Firefox as well as Chrome crashes after a few minutes of surfing and Norton shows me these (links to images):

Errors
Norton analysis

I analyzed firefox.exe and chrome.exe with Norton but nothing was wrong with these. Since this happens wit different browsers I believe there is no problem with a single program but rather an "attack" from the outside.

Can anybody help?

Thanks a lot.