I do not know if this is default behaviour on all platforms, but when middle clicking on a web page in Firefox, it will load the URL on the clipboard (if any). I find this pretty annoying, because I use middle clicking a lot to open URLs in new tabs. Making a miss click potentially erases an entire form I had been filling out (you can guess I actually just had this happen). Luckily like just about everything in Firefox, you can customize this behaviour!

Just go to good old about:config and change the value of middlemouse.contentLoadURL to false by double clicking on it. In a quick and easy fix as that, my clumsiness will no longer be punished dramatically.