If you're using a Windows Operating system, it already has a pre-installed antispyware program on it.. "Windows Defender" although not a perfect tool, already scans for spyware and other similar types of malware.. It does NOT scan for viruses and worms.. As such, you need an antivirus programs such as Norton, or the new version of Webroot.. Unfortunately, BOTH of those programs ALSO scan for spyware, plus viruses.. All those scanners performing similar types of real-time protection frequently get in the way of each other..

So...Uninstall one or the other, then see if it helps the problem with the browsers.. Make sure Windows Defender is disabled so the other tools don't stumble over it.. If the problem still occurs with your browser, then uninstall the other antivirus/antispyware scanner to test whether the problem is fixed.. If uninstalling both of them seems to fix the problem, then maybe your computer needs a program that uses less memory/resources.. Trying one of the free antivirus programs below might then take care of the issue.:

AVG
http://free.avg.com/us-en/download-free-antivirus

Avira
http://www.avira.com/en/avira-free-antivirus

Avast
http://www.avast.com/free-antivirus-download

To read another thread which has symptoms that are much like your problem, see the link below:

http://forums.cnet.com/7723-6122_102-526584.html?messageId=5131109

Hope this helps.

Grif