It’s a question I’m asked fairly often, and my response is usually “it depends”. addons.mozilla.org (AMO) is a pretty complex system, so answering a simple question like “how many add-ons are there?” isn’t so easy when you consider that there are 7 types of add-ons, different status levels, and several supported applications. And of course, not all add-ons are hosted on AMO. My answer to that question to someone looking for consumer-friendly Thunderbird add-ons would differ by thousands from my answer to a web developer who wants to extend Firefox to its fullest.

A few weeks ago I had the idea of a self-service chart that I could point people to when they ask me this question, and here it is.

(I strongly recommend viewing this table on my blog.)

Add-ons hosted on AMO (June 12, 2009)
		Status
		All	Active	Active Public
Add-on Type	All	10936	8661	3531	All	Application
		9140	7640	3061	Firefox
		978	848	543	Thunderbird
	Extensions + Themes	10046	8021	3271	All
		8946	7479	2965	Firefox
		843	737	469	Thunderbird
	Extensions	8937	7248	2803	All
		8065	6792	2567	Firefox
		746	664	407	Thunderbird

Some explanations:

• The status row is made up of 3 columns: All (every single add-on in the database), Active (neither user-disabled, admin-disabled, nor “incomplete”), and Active Public (active and the add-on has “public” status, meaning it has been reviewed by AMO Editors)
• The add-on type column is made up of 3 rows: All (every add-on type: extensions, themes, dictionaries, search plugins, language packs, plugins), Extensions + Themes (only extensions and themes are counted), and Extensions (only extensions are counted)
• The application column is made up of 3 rows: All (every application AMO supports: Firefox, Thunderbird, Sunbird, SeaMonkey, Fennec), Firefox, and Thunderbird. Keep in mind that some add-ons are compatible with multiple applications.

I didn’t want to make the table even more confusing, but if you’re interested in other applications: 324 active SeaMonkey add-ons, 99 active Sunbird add-ons, and 33 active Fennec add-ons. And other add-on types: 119 active dictionaries, 470 active search plugins, and 51 active language packs.

Please don’t ask me to break this down by Firefox 3.5 compatibility — I think my <table> might explode.