Maybe that mouse is on its last legs?? IMO, the first thing to rule out.

I've had that happen with a few different mouses over the years; the contact was almost worn out and it was bouncing, creating a double-click or a triple-click and causing multiple tabs to be opened.

Its not my mouse... or at least I don't think it is. It may be something with the cookie settings... When I click on some links in Twitter or on Facebook two tabs are opened with the same content but I don't seem to have the problem if I set the Privacy option: "Accept third-party cookies" to: 'never' ...

Oeps... thats not true... I will try another mouse...