From MozillaZine Knowledge Base
Once you have created an extension, share it with the community!
There are a few major sites that list extensions for Mozilla products. The most popular and most important one is the official addons.mozilla.org. Other web portals such as erweiterungen.de list extensions that are available in certain language (such as german e.g.). There is also an Extensions forum at MozillaZine, where many authors announce their extensions and ask for help.
After submitting your extension to addons.mozilla.org it might take severals days or weeks until your extension will be reviewed (and approval will be granted). this is important to keep the quaity of the extensions high and prevent the mozilla user community from malware extensions.