Well i have pretty much all those listed, but as to not repeat here's a couple i really like to add:
answers - gives definitions of words with alt+click
all in one sidebar - a quick sidbar view for downloads, dialog menus, etc
download status bar - put all your downloads in a nice status bar inside FF
No Script - prevents any and all scripts from running (can be disabled on a page by page basis) this extension notifies you if a scritpt wants to run