I like Firefox's extensions.  IE is so bloated, because everything's built in...and it still doesn't do the things Firefox can. 

My favorite extensions:

Ad-Block.  Install Ad-Block and the Filterset, and 80% of the ads on the net vanish. Popups, pop-unders, banners, etc. - gone.  I also recommend Ad-Block Plus.

IE Tab - allows you to open a link in an IE tab.  For the roughly 1 out of 50 sites that doesn't display correctly in Firefox.

NoScript - prevents scripts from running, unless you permit it.

Flashblock - blocks Flash, unless you permit it.

DownloadThemAll - a mass downloader.  I've been able to download files with this that I couldn't download the usual way.

Text size Toolbar - let you adjust text size with a click.

Colorzilla - allows you to get the RGB coordinates of any color you click on.  So if you want the background of your image to precisely match that mint-green hue DAZ uses as a background color, you can.

BBCodeXTra - allows you to easily add links, images, quotes, etc., on HTML or BBCode message boards.