The most popular alternative web browser. Some websites are reporting that more than half their visitors are using Firefox. Though the actual percentage is much lower, this indicates a very high percentage of more technical users love and use Firefox.

It is clean and simple, more secure than Microsoft Internet Explorer, and its functionality can be easily extended and customised.

Useful Firefox Extensions

Firefox's functionality can be extended. Here are some extensions I use:

Google Gears
gears,google.com
Allows offline access to web services that support it.
Including: Google Docs, Google Reader, Remember the Milk, Zoho Office

Google Notebook Extension
http://www.google.com/tools/firefox/
Gives you easy access to Google Notebook.

Delicious Buttons
https://addons.mozilla.org/en-US/firefox/addon/1532
Integrates Delicious' tagged bookmark system into Firefox.

Diigo Toolbar
http://www.diigo.com/tools
Integrates Diigo's bookmark and comment system into Firefox.

Remember the Milk Gmail extension
http://www.rememberthemilk.com/services/gmail/
Puts a to do list next to your mail in Gmail.

GTDInbox
http://www.gtdinbox.com/
Lets you organise your email with GTD, David Allen's Getting Things Done system.

Lifehacker "Better" Firefox Extensions
http://lifehacker.com/397940/better-firefox-extension-updates-now-available
- better gmail2
- better gcal
- better greader

Other Extensions

These look promising, but I had trouble with them or didn't think they were quite for me at the moment.

AutoPager
https://addons.mozilla.org/en-US/firefox/addon/4925
Automatically loads the next page of a site while you are scrolling.
Looks promising, but crashed Firefox for me. Perhaps it's not compatible with one of the other extensions.

Gmail Signatures
http://blankcanvasweb.com/pages/detail/id_9/n_gmail_signatures/
Multiple html signatures per google account.