Here's my list of extension I use in Firefox 3. I can confirm that they are available and working properly:
- Adblock Plus 0.7.5.4
- Answers 2.2.48
- ColorZilla
- DownloadHelper 3.0.4
- Firebug 1.2.0b2 (see my post on this)
- lori (Life-of-request info) 0.2.0.20080521
- MeasureIt
- Password Exporter 1.1
- StumbleUpon 3.18
- Twitterfox 1.5.5.2
- YSlow
- Web Developer 1.1.6
- del.icio.us
- foXpose
- Paste and Go
- PicLens
- zoomFox (although this one has no real use anymore because of the tremendous new zoom feature available in FF3)