I have used roughly 40 firefox extensions since it came out and thought I’d share my favorites. I am running 3.0.5 on OSX 10.5.5 
AdBlock (duh!)
Since I hate ads, adblock saves the day for me. Most people know this and love it. I have further capitalized on the brilliance of this extension but creating some custom filters to block the video ads on hulu.com and fancast.com. In some cases its like the commercials never existed, in others there is just a “you blocked our ad…” screen for 30 seconds before the video resumes.
Web Developer (cur. version 1.16)
As a web developer, anything that simplyfies things and speeds up tasks is a huge help. This plugin gives you a wide array of tools to help debug your work. My favorite features are the live html editing and the “show passwords” for obfuscated form entries.
Quartz PDF plugin
This finally came out a month or two ago, allowing users running OSX 10.5 and FF3 to open pdf files natively in the browser. This is a HUGE timesaver!
GMail Signature
Using multiple accounts with gmail is a great feature. Only having the option to use 1 signature is not. This plugin gracefully solves that problem allowing you to have up to 4 signatures per “from” address. Rich html signatures and a live preview make this addon a must-have for gmail users.
