My mouse is wearing out. It's a specialized mouse, so I don't want to replace it every 1-2 years. The top button often gives extra clicks. The middle button doesn't. My mouse has button-mapping software, so I switched the top and middle buttons. I used the middle button with my scrolling software, along with the left-side buttons, and the extra clicks shouldn't affect something which relies on holding the button. But ... for some godawful reason, Firefox closes a tab if people use the middle button to try to switch to the tab. Or in my case, if I try to use the top button. I can't even find an about:config setting to stop this!