Here’s the extensions pages for mozilla.
Extensions extend the functionality of a program like FireFox. FireFox is a browser, a good one at that. I have been smitten by its tab function. Not a new idea but it is a new idea when implemented in a browser. I know I’ve always used tabe extensively when I would make Java applets. Here’s a Java Applet I made.
For example, ever get tired of constantly refreshing a page? Well, you can use the page refresher/reloader extension for FireFox. It automatically refreshes your page. Now that can be handy, especially if you are on a forum that doesn’t give you alerts if someone has posted to your reply and you’re basically there fishing for the next answer or reply.