mine is wired too and does that all over the place, not real often anymore though now that I updated the driver a bit. It doesn't sound like a mouse problem you have though if it's only in the browser, and doesn't happen to me in any of the browsers so I'll assume this may be a Win7 issue.
I use Windows 7 and IE 8 with a wireless mouse on my Toshiba laptop and I have no issues.