You already know you can open a link in a background tab by clicking it with your mousewheel, but the TechMalaya.com site points out five other mousewheel Firefox tricks that you may not have known. Like this gem, which requires a change to about:config:
Change the value of middlemouse.paste to true. This will let you paste a clipboard content to any text field with the middle mouse button.
Using this tweak coupled with the beloved AutoCopy extension, you could select text on-page and paste it into a textarea (like in a comments response) with a simple click, drag, and mousewheel hit. See more of our favorite Firefox 2 about:config tweaks.