hello girliegig, yes the absolute majority of addons is coming from third-party developers. mozilla is developing/providing a few extensions itself though (mainly dictionary packs): https://addons.mozilla.org/firefox/user/mozilla/

Extensions and Themes hosted at addons.mozill.org goes through a review process.

Toolbars are one type of extensions you may want to be more careful about and avoid any that mentions the word conduit anywhere especially or even ones that has a privacy policy.

The word Addons does not refer to just Extensions as it also groups together Themes (both complete and background images aka Personas) , Plugins, and even dictionary, language packs, search engines are included.

Thanks Phillip and James for the info and super fast reply!

Oops, sorry - Philipp :)