I recently added some new (for me) Firefox add-ons. I love this one...

http://interclue.com/

You can just hover your mouse over a link and an icon will appear. Hover the mouse over the icon and a window pops up with the linked page in it. You can scroll up and down in the page just as if you had clicked on the link. It's a somewhat abbreviated version of the page, but most of the information is there. I checked to see if it's possible to click on links inside the window, and you can't do that (but it would be very weird and interesting if you could).

I also added one that allows me to open a page in IE in a tab in a Firefox window. I like that one a lot, too, because with that one I am able to have two different Yahoo accounts (for instance) open at the same time in the same window (because they're in different browsers). That one's called IE Tab.

Another really cool one that I added is called Image Zoom. That one lets me zoom an image in a page just by hovering my mouse over the image and simultaneously pressing the right button and scrolling the wheel.