Review for Extension Manager Extended by harkabeeparolus
Rated 3 out of 5 stars
As an alternative, I would suggest the Firefox / Thunderbird extension "MR Tech Toolkit", which does all this and much more. It's been around for a very long time, so it's quite stable, and has tons of features without feeling bloated.
This review is for a previous version of the add-on (2.8).To create your own collections, you must have a Mozilla Add-ons account.