No... this happened simultaneously on all three browsers. I have safari, chrome and firefox installed. I checked on all immediately when I encountered it. In one I was logged in [vbulletin] and the other 2 I wasn't - it happened on all 3. I don't think I have ever installed Google Toolbar - and definitely not on all three. It could be the Google notifier but that's a mac app not related to the browser.
I'll notify if it happens again. It seemed to happen after a period of inactivity.