Hopefully that title isn't too confusing. I wasn't exactly sure how to word it as this has never happened before. Anyway, like I said, middle-clicking on a link to open it in a new tab will sometimes copy the URL of the link I was trying to go to, and enter it as a search term in Google. It's the weirdest thing I have ever seen in Firefox. For example, say I was on another website and middle-clicked on the URL for Mozilla's support page. But instead of going to Mozilla's support page, I'll wind up on Google, with the URL "http://support.mozilla.com/" as the search query. It's difficult to try and recreate this bug. It just seems to happen at random times, though it does happen frequently, and only when I open a tab using the mouse-wheel.