I have added a few things to my Firefox lately, so here are some of the icons that are sitting on the toolbar

 Stylish.  This plugin works very similarly to Grease Monkey, I am using this right now because they have an awesome redesign for Gmail which allows me to use Gtalk and AIM from work through Gtalk. 

 Meebo.  This one adds little notifications (similar to guifications for PIDGIN) to Firefox for Meebo which makes Meebo just that much better, this way you know when you get IM’s regardless if you are focused on Firefox or not.

 IE Tab. nothing new been using this one for a while

 Foxmarks.  This one is amazing because it syncs all my computers Firefox’s bookmarks making bookmarks actually something that I use. 

 Fast Video Download.  This allows you to download any YouTube video with the click of a button.  It downloads the file a .FLV

Autocopy.  Nothing new here have been using this one for a while.