I don't know any of those, Gilly - what do they do?
I like Downthemall, IE tab and Adblock as well
Greasemonkey- The best extension available. Install it and then go to userscripts.org to find scripts to make websites better. My favorites are Facebook and Google Image scripts that enlarge thumbnails to full size when you mouse over them.
PicLens- Really cool extension that lets you scroll through (like Ipod coverflow) Google Image, Flickr, Youtube, and a bunch of other sites. This one is only going to get better.
FireGestures- Lets you use your mouse to gesture to do anything Firefox is able to do. For instance, I hold right click and move my mouse to the left and it goes back a page. Hold right click and move mouse down to bring up bookmark sidebar. It's all customizable.
SageToo- RSS reader
OpenSearchFox- Right click on any search bar and add it to your search bar in your navigation toolbar (the Google search)
Googlepedia- Adds a Wikipedia entry to Google search on the right hand side.