I really love this feature of the Tab Mix Plus Addon for Firefox.
I use Shazam on Online-Sweepstakes.com and I have a lot of tabs open at any given time. I move pretty fast. Sometimes I click too quickly - close a tab and have no idea what I just closed. I just chalked it up to my stupidity and missed that daily entry for the day. But if you are using Tab Mix Plus, there is an easy way to figure out what Tab you just closed.
Just right click anywhere - A menu pops up - and on the menu you will see "Undo Close Tab"
Presto! That daily is back in play!
Another great feature is "Duplicate Tab" Right click on any tab label and you can open a duplicate of that tab. I've found this useful when entering blog entries, you can keep one tab positioned to enter the comments, and one tab positioned to read the gazillion ways to earn extra entries.