Mozilla Add-ons

Mozilla Add-ons is the official Mozilla website to store add-ons for Mozilla software. This software includes Mozilla Firefox, Mozilla Thunderbird, SeaMonkey, and Mozilla Sunbird.
These add-ons include extensions, themes, dictionaries, search bar "search engines", and plugins.
History.
Mozilla Update (UMO, update.mozilla.org) is the oldest name of Mozilla Add-ons. AMO is a non-official name for Mozilla Add-ons today.
Structure.
Add-on developers are thousands of volunteers. Not Mozilla employees. After an upload, add-ons are reviewed. If accurate, they're published.