Review for MinimizeToTray by truello
Rated 5 out of 5 stars
The 6 steps DO work. Those of you who couldn't get it to work were probably not editing the file in edit mode, but a temporary file which never gets put back into the zip.
Rename .xpi to .zip, extract the zip, edit the file, rebuild the zip, rename to .xpi then install.
To create your own collections, you must have a Mozilla Add-ons account.