Iceweasel is a PLD effort to create freely distributable version of Firefox web browser. Iceweasel is almost completely compatible with Firefox. Most add-ons designed for original application will also work with this one.
NOTE: PLD Iceweasel differs from Debian project with the same name.

There are many useful extensions on mozdev.org. Make sure to check whether the add-on is compatible with Firefox and is not specific for Windows platform. You should be able to install most of them in your personal directory.