Once you have a first build of your add-on, you'll want to distribute it so others can give it a try. Whether you are distributing your add-on publicly or privately, through addons.mozilla.org (AMO) or elsewhere, you'll want to have your add-on package signed.
Signing your add-on
Starting with Firefox 41, there are some restrictions for add-on distribution. Extensions and multipackage installers that support Firefox need to be signed by Mozilla in order for them to be installable in release and beta versions of Firefox. Note that this only applies to add-on types 2 and 32; other add-on types like themes and language packs don't require signing. Add-ons that only support other applications like Thunderbird and SeaMonkey are also excluded. Unsigned add-ons can still be installed in Developer Edition, Nightly, and ESR versions of Firefox, after toggling a preference.
Only Mozilla can sign your add-on so that Firefox will install it by default. Add-ons are signed by submitting them to AMO and passing either an automated or manual code review. Note that you are not required to list or distribute your add-on through AMO. If you are distributing the add-on on your own, you can choose the Unlisted option and AMO will only serve as the way to get your package signed.
Submitting to AMO
Next, you'll need to decide if you want to distribute and list your add-on through AMO or not. Here are some things you should consider to make this decision:
- AMO is a very popular distribution platform, with millions of monthly visitors and installations. It is integrated into the Firefox Add-ons Manager, allowing easy installation of published AMO add-ons directly from the Firefox UI.
- All add-ons listed on AMO are code reviewed and tested by a team of employees and volunteers. They need to meet various technical and content policies in order to be accepted. Because of this, review times can range between a few hours to a number of weeks, depending on add-on complexity and other factors.
- Unlisted add-ons are for the most part automatically reviewed and signed. If an add-on doesn't pass automatic review, then it's moved to a review queue where it should be reviewed within a couple of days. If an unlisted add-on requires side-loading (bundling with an application installer rather than the usual web install), then it needs to be code reviewed, which may take up to a couple of weeks to be completed.
- Add-ons listed on AMO can only be updated through AMO. External update mechanisms are not allowed. Unlisted add-ons, on the other hand, need to be updated on their own.
An add-on can be changed from Listed to Unlisted and viceversa, if you change your mind. You should know that if you switch from Listed to Unlisted, your current users won't be automatically migrated to the unlisted versions of your add-on. Switching from Unlisted to Listed is easier because Firefox will check for updates on AMO if an add-on doesn't have an updateURL in its install manifest.
Due to technical limitations on AMO, add-ons can only have their visibility changed by deleting the add-on and submitting it again.
After accepting the Developer Agreement, you'll be asked if you want to list your add-on on AMO. Make sure you choose not to list it.
You'll then be asked if you want your add-on to be side-loaded or not. Side-loading is when your add-on XPI isn't installed directly by users but instead it is bundled in an application installer. An example of this would be an antivirus software package that includes a companion security extension. If your add-on XPI will be installed directly from the web or downloaded and installed manually by your users, then you don't need this option.
Internally, AMO labels unlisted add-on submissions that require side-loading as Full Review submissions, and all the rest as Preliminary Review submissions. You may find these labels when looking at your add-on review status. Note that there's no difference between full and preliminary review for unlisted add-ons, other than the ability to side-load the add-on.
Choose the platforms your add-on supports and upload your XPI. The file will be scanned by an automatic code validator which will show a number or warnings or errors depending on what it detects. If no errors are found and you didn't choose the side-loading option, your add-on listing will be created and your file will be immediately signed. You'll receive an email with instructions on how to download the signed file. If your add-on doesn't pass validation or you chose the side-loading option, you'll have the choice of submitting your add-on for manual code review. Once the add-on is reviewed by a member of our team, you'll receive an email explaining if it passed and was signed, or if it didn't, including the reasons why.
Note that failing automatic validation doesn't mean your add-on is unsafe or unfit for signing. Many of the tests the validator does are broad and can lead to false positives, which is why there's a manual code review fallback. However, you should carefully read the validator output and see if there are any alternative APIs or coding patterns you can use to avoid errors and warnings. This doesn't mean that you should obfuscate your code to bypass validation. That practice can lead to your add-on being rejected and potentially blocklisted.
All new versions of your add-ons will also need to signed. Once your first version has been submitted, you can upload new versions in the developer page for your add-on. The process is the same, starting with automatic validation and potentially a manual code review.
After accepting the Developer Agreement, you'll be asked if you want to list your add-on on AMO. Listing it should be the default option.
Choose the platforms your add-on supports and upload your XPI. The file will be scanned by an automatic code validator which will show a number or warnings or errors depending on what it detects. Errors only show up for listed add-ons if there's something wrong in the package that needs to be fixed before it can be accepted. Warnings can vary in importance and severity; you should read through all of them carefully and see if there's anything you can fix in your add-on in order to avoid them showing up. This doesn't mean that you should obfuscate your code to bypass validation warnings. That practice can lead to your add-on being rejected and potentially blocklisted.
Once you finish your listed add-on submission, it will be placed in a review queue, where one member of our review team will eventually give it a look. This can take between a couple of hours to a number of weeks, depending on add-on complexity and other factors. It also takes longer for the first submission, since all of the code needs to be reviewed. Updates are reviewed based on a diff, so they are quicker. Once your add-on passes review, the file is signed and published on AMO.
Listed add-ons can be submitted for Preliminary Review or Full Review. Preliminary Review consists on security and content checks, focused on the add-on's code. Full Review is a higher standard, and reviews include feature testing and performance checks. Add-ons with Full Review have more prominence on the site and be nominated to be featured. Add-ons that are nominated for Full Review and don't meet that standard may receive Preliminary Review approval instead.
Beta channels are only available to fully-reviewed add-ons.
To create a beta channel, upload a file with a unique version string that contains any of the following strings:
a,b,alpha,beta,pre,rc, with an optional number at the end. This text must come at the end of the version string. If you understand regex format, here's what we look for in the version number:
Once a file meeting this criteria is uploaded to AMO, it will automatically be detected as a beta version. Users of add-ons with these unique version numbers will automatically be served the newest beta updates.
Beta versions are treated like unlisted add-on versions, in that they will be accepted and signed immediately only if they pass automatic validation. If they don't, there will be an option available to submit it for manual review.
While we call these "Beta versions", you can use this channel for nightlies, or alphas, or prerelease versions as you wish. Please note that there is only one channel for this purpose and all of your users on this channel will receive the latest add-ons submitted. For instance, if you upload
1.0beta1 to the release channel and then upload
1.1alpha1, all users of
1.0beta1 will be offered an upgrade to
1.1alpha1. Updates are pushed by submission date and not version number, so users will always get the most recent channel update regardless of any kind of alphabetical sorting.
Add-ons can have multiple users with permission to update and manage the listing. Existing authors of an add-on can transfer ownership and add additional developers to an add-on's listing through the Developer Tools provided. No interaction with Mozilla representatives is necessary for a transfer of ownership.
Many add-ons allow their source code to be openly viewed. This does not mean that the source code is open source or available for use in another add-on. The original author of an add-on retains copyright of their work unless otherwise noted in the add-on's license.
In the event that we're notified of a copyright or license infringement, we will take steps to address the situation per the DMCA, which may include taking down the add-on listing. Details about this process and how to report trademark or licensing issues can be found here.
If you are unsure of the current copyright status of an add-on's source code, you must contact the original author and receive explicit permission before using the source code.