Review for MinimizeToTray by Spacetech
Rated 5 out of 5 stars
If you want this extension to work for firefox 3 download http://www.mrtech.com/extensions/local_install/ and when you install minimizetotray check the "override 'max version' compatability checking" checkbox. It works fine!
To create your own collections, you must have a Mozilla Add-ons account.