Firefox Plugins

There are a number of useful firefox add-ons:

No Script

an add on to control easily whether scripts (java, javascript, flash) are allowed to be performed. This is a per domain enabling or not.

Download Them All

with this add on, it easier to download many resources from a web page

Download Status Bar

adds a status bar which shows the status of downloading of things from firefox.

Greasemonkey

using greasemonkey allows to write scripts to be performed on top of web pages

Firebug

This is a utility to help in developing javascripts.