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Add-on Reviews

The Queues

The add-on queues are sorted by waiting time, with the longest waiting add-on at the top. They show the same information for every pending review:

  • Add-on name and version. This is a link to the review page. A lock icon next to it means that another editor is looking at this review page.
  • Add-on type.
  • Waiting time.
  • Flags.
    • Admin Review flag: it's the green add-on icon with a yellow warning sign on top. Only admin editors can review add-ons with this flag.
    • Pending info request: a blue icon with an 'i' in the middle. An editor has requested additional information from the author. Authors will reply to the mailing list and another editor will take care of it.
    • Jetpack: the add-on was created with the Add-ons SDK.
    • Bootstrapped: the icon is a green circular arrow with a red X on it. It means the add-on is bootstrapped (doesn't require a restart to install) but not an SDK add-on.
    • Editor comments: a user icon with a speech bubble. The comment should be read carefully since it's usually very important.
  • Applications. The applications this add-on supports.
  • Platforms. The platforms this add-on supports.
  • Additional information. This can indicate if the add-on is platform-specific, site-specific, or requires external software.
  • Version notes. The icon on the far right will show you the Version Notes of the pending version, giving you an idea of how simple or difficult the review will be.

You should always try to review the add-ons near the top of queue. Always favor the add-ons that have been waiting for the longest time. Having said that, the few add-ons that are at the very top and have been waiting for a much longer time than the rest (sometimes multiple days more than the next one) are likely to be add-ons that require special review from an admin editor, or are awaiting a response from the developer. Try to focus on the first 10 or 15 add-ons in the queues. There should be a couple there that you can review.

Performing a Review

Before getting started, here's an important legal note: reviews must not involve checking for copyright or trademark violations and you should not take any action on an add-on because you suspect it copies code from others without permission or may otherwise infringe somebody else's copyright or trademark. The DMCA is a law that gives us legal protection from being held responsible for copyright infringement by users who post content to our site, but only if our conduct qualifies us for such protection and we follow exactly the procedures laid out in the DMCA. Determining copyright or trademark infringement is complicated and you will not have enough information to make those determinations. We have a robust DMCA process where copyright or trademark holders can contact Mozilla legal to address any potential problems.

Editor Tour: Select any review in the Full Review Queue and click on its link. This will take you to the add-on review page. Do not save a review for this add-on without asking your admin guide first!

Possible resolutions

The button set at the bottom of the review page shows all possible resolutions for a review.

Possible review resolutions

Clicking on any of them will open a form below it.

The comments textbox is where you should write all of your review notes. There's also a canned response list below it, that contains useful reusable snippets of text for your notes. Selecting any of them will just add the text to the textbox. You can use as many as you need.

Take some time to familiarize yourself with the canned response list. It can give you a good idea of the issues we frequently encounter and what we have to say about it.

You should normally use one of the first three resolutions:

  • Push to Public: the version doesn't have any problems and it's OK for the public.
  • Grant Preliminary Review: the version has problems that prevent us from making it fully public, but it is still safe to use.
  • Reject: the version has security issues and must be rejected.

The other 3 are used on special situations:

  • Request More Information: this allows you to ask the author for information necessary to perform the review, without removing the add-on from the queue. A very common case for this is when the add-on is site-specific and the author didn't provide a test account. Since we can't be registering to every site on the web just to test, we ask authors to provide the necessary information.
  • Request Super-Review: this is for very special cases where you think an admin editor should review this add-on. It can be because you think there's some malicious intent from the author; in this case you should also notify the mailing list about it. It can also be because you are aware Mozilla has received a DMCA notice about this add-on. It is critical that you do not try to resolve this issue yourself. Copyright complaints should be escalated to admins and, at most, you can point the person making the complaint to the Digital Millennium Copyright Act Notice section of our legal notices page for an explanation of the protocol to follow. The add-on will remain in the queue, and in this case the comments aren't sent to the author. They're only readable from the review page.
  • Comment. This allows you to add a comment that is only readable by other editors. It can have testing information, partial notes that you had from reviewing a version that you couldn't finish, etc.

While you perform your review, you should be keeping notes of everything you observed about the add-on: code validation flags, errors in the error console, bugs, areas for improvement, etc. You can either use a note-taking program, or just type your notes in the comments textbox of the review page. Changing the resolution won't clear your notes. Just make sure you selected the right resolution when you're ready to submit!

The sections below include tables with the recommended action for the most common situations. If there are more than one policy problems in a review, you must take the strictest of all required actions.

Editor Tour: request your admin editor to point you to an add-on to review. Don't submit your first review without their pre-approval!

Step 1: Review Add-on Info

The review page has most of the add-on metadata needed to begin the review.


The top section is very similar to the public add-on listing on AMO. It shows it descriptions, author info and rating. It also include links to the Privacy Policy and EULA, both of which are important to review. The add-on must respect the conditions stipulated in those documents.

Below the descriptions you should see the review history (called Add-on History on the page). The history contains all previous reviews done on the add-on, including the version notes, notes to reviewer, comments and editor notes for each one of them. This is very valuable information, and you should always read at least the most recent reviews.

Policies and Actions

Policy Action Notes
Empty name (the name is blank in default locale) Request More Information Reject if the name is not updated after 3 days.
Missing information in descriptions, missing testing information Request More Information
Add-on name and code copied from very popular add-on (like Firebug or AdBlock Plus) Admin Review / Notify mailing list These add-ons can include some form of malicious code and trick users into thinking they are the original one.
Add-on name or icon identical or very similar to existing, active listing Admin Review We want to avoid user confusion when selecting which add-on to install. It's OK to fork, but it should be clear what are the differences between very similar offerings.
Other copyright suspicions Ignore We have a legal obligation *not* to take action unless the author of the original code files a DMCA complaint. If you see any malicious intent in the copied add-on, follow the same Action as the previous policy.
Not compatible with the current versions of the application Add note There's a canned response for this purpose. Reject if the maxVersion is lower than 4.0, unless it's a critical fix.
Missing Privacy Policy or EULA when necessary Preliminary Review These descriptions are necessary if the add-on handles user information remotely, or the user needs to agree to any terms in order to use the add-on.
Questionable add-on relevance Preliminary Review Carefully read the Add-on Relevance section below. This policy should only be enforced on extreme circumstances.
New version doesn't follow previous editor requests Preliminary Review If the author keeps submitting the same version, contact the mailing list.

Add-on Relevance

Add-on relevance should only matter if the add-on is obscure or difficult to review, or you think that it is too simple to be fully approved. In general you shouldn't make any assessments on add-on relevance, since we have download counts, active daily users and user reviews to rank all add-ons on AMO.

We have a very low admission threshold, but we don't want to fully publish add-ons that will get at most a couple hundred downloads and will be mostly ignored during their lifetime. In that case, the add-on should at best receive a preliminary review approval.

Add-ons that commonly fall into this category are:

  • Add-ons that help access very specific webpages. For example, an add-on that makes it easier to use an internal business site or a university library.
  • Add-ons targeted to a limited geographical area. For example, an add-on for a local city newspaper or radio station.
  • Add-ons that only add a toolbar or menu filled with website links, similar to plain bookmarks.
  • Add-ons that download video files from Flash video sites like YouTube. We already have too many add-ons like these, with little to no distinction between them. Unless the add-on provides something really innovative to video downloading, it should not get full approval.

Assessing the relevance of an add-on can be difficult. In these cases you should leave the review to somebody else or ask on the mailing list.

Step 2: Automatic validation

We have a extensive set of static tests that identify common bad practices and possible security problems with add-on code. You must always run the code validator and inspect the results when performing a review.

Each Add-on History entry has a validation link. You'll want to validate the latest version.

Add-on validation link

Clicking on the link will take you to the validation page, where the automatic code validator will run for that version of the add-on and then the results will be displayed. It's usually best for navigation to open this link in a new tab.

Policies and actions

Policy Action Notes
Missing file / Parse error / Validation error Reject
Obfuscated, minified or binary code Reject There's a canned response for this.
Obfuscated, minified or binary code, with original sources included in XPI or provided link Admin Review
Using eval, Function(), setTimeout, setInterval to evaluate remote code Reject
Remote script injection Reject
<browser> or <iframe> elements with no type Reject See canned response and iframe documentation. If the frame or browser is used to load chrome content, it's fine as long as that's clear from reading the source.
Inserting remote content with innerHTML Reject If it's only local content, Add a Note to fix it on future versions. There's a canned response.
Using DOM Mutation events Preliminary Review Just add a note if this is a first warning and the add-on has been approved with this code before.
Conduit add-on without CONDUIT-AMO as author Reject
Conduit add-on with CONDUIT-AMO as author Admin Review
JS Library (like jQuery) included, but not in its original file. JS Library doesn't pass checksum validation. Reject
Unicode characters (e.g. \u0060) in JS code Reject Keep in mind these can be used safely inside strings. They're just not allowed to replace characters in JS code, since they can be used to bypass the validator.
Using eval, Function(), setTimeout, setInterval to evaluate local code Preliminary Review One case that we accept is when eval is used to replace existing Firefox functions. This is very common for add-ons that change bookmarking or tabbing behavior. It is also allowed in known libraries like jQuery.
Using the codebase_principal_support preference or enablePrivilege function Preliminary Review They're deprecated.
Native object prototype extension / Using Prototype library Preliminary Review
Storing passwords or other sensitive user data in the preferences Preliminary Review
Changing Firefox preferences without user consent Preliminary Review These include: network preferences, update system preferences, homepage, User Agent string.
Changing security preferences, permissions, certificates (nsIX509CertDB) Admin Review
Using nsIProcess Admin Review
Using JS c-types Admin Review
Using Geolocation Test Give Preliminary Review if the add-on doesn't ask the user for permission to use geolocation before getting geolocation data (this is how users should be asked for permission). Approve if it does.
Localization errors Ignore

See the security code review page for more detail on the above security rejection reasons.

Most of the other validator flags are not that important, but they should still be fully read and understood. When in doubt, check the help page or ask in the mailing list.

Step 3: Code Review

Every line of add-on code must be reviewed. The code validator can't detect all possible security or code quality issues, so we must always be on the lookout for bad code. For versions in the Preliminary Review queue, the code review should just ensure the add-on's safety.

All review pages have a View Contents link that take you to the code browser page. Pending updates also have a Compare with Public Version link next to it, which will show you the code with the changed sections highlighted.

For updates, the compare link should be used. However, it can sometimes fail to work for very large add-ons. In that case, you can either review the full source code, or download the new and public files to your system and compare them using tools like or WinMerge.

Validation results are integrated into the code viewer, so you can see validation warnings in context. For Add-ons SDK extensions, known library files are shaded in grey, and their origin is stated in the popup that appears when hovering over them.

Policies and Actions

Policy Action Notes
Remote code download or execution, custom update code Reject Add-ons should not download remote code in any way. They are free to interact with web APIs as long as all that is being transmitted is data, not code. Add-ons are allowed to insert local scripts into webpages (within reason), but are not allowed to insert remote scripts.
Modified on unverified Add-ons SDK library code Reject Library files that are unrecognized will not appear in grey color.
Using non-release Add-ons SDK library Preliminary Review The validator can detect many experimental versions of the SDK, but that doesn't make it OK to use in public add-ons. Public add-ons should use release or beta versions of the SDK. Others should only get preliminary review.
Using outdated Add-ons SDK library Preliminary Review Except under special circumstances, we accept the two most recent minor releases of the Add-on SDK. If the validator warns that the add-on is using an outdated SDK version, it is acceptable for full review if it is one release older than the suggested release. Otherwise, it is only eligible for preliminary review.
HTTP security violations Reject Sending passwords over unprotected HTTP if there's a secure alternative. Sending passwords in the URL or other headers than POSTDATA. Performing any security-sensitive operations over HTTP when there's a secure alternative.
Bad or no namespacing Preliminary Review All scripts that are included in the main window overlay should have proper namespacing to avoid name conflicts with other add-ons. The name should normally correspond to the add-on name in order to guarantee its uniqueness.
Preference names without "extensions." prefix Preliminary Review (nominations only) Add-on preferences should use the "extensions." prefix, and should also have a reasonable namespace. If the add-on is already public, this rule should be ignored.
Extension preferences names in Sync without "services.sync.extensions." prefix Preliminary Review Add-on preferences using the Sync service of Firefox should use the "services.sync.extensions." prefix, and should also have a reasonable namespace.
Privacy issues Preliminary Review An add-on can claim to work with a popular website like Twitter, but then send the user data through some other site, most likely owned by the developer. There needs to be a justified reason to handle user data in this manner, and the privacy policy and add-on descriptions need to be very clear about this. Passwords should never be handled in this way, and they should only be transmitted directly to the original API provider.
Performance problems Preliminary Review Synchronous requests, noticeably inefficient code, random UI freezes, loading large amounts of JS code (in the order of tens of thousands of lines of code) directly in overlays.
Not using prefwindow for preferences Add Note If an add-on has a preferences window, we recommend that authors do 2 things: 1) use the prefwindow element, 2) add the line in install.rdf that enables this window to be opened from the Add-ons Manager window.
Duplicate / hidden files or folders Add Note See canned response.
Unpacked add-on writes files in own installation directory Preliminary Review Writing in the installation directory can generate problems with the Add-ons Manager, where the add-on can be stuck in an update loop. Add-ons should write all files in the profile dir.
Bootstrapped Add-on doesn't clean up after itself Preliminary Review See section on Bootstrapped Add-on policies.

See the security code review page for more detail on the above security rejection reasons.

In general you should apply your judgement and try to identify code that may appear suspicious or out of place. Try to understand what everything does and how it all fits together.

By the end of the code review, you'll may have a series of notes that will require the add-on to be significantly rewritten. If you think that's the case, it's OK to resolve the review without proceeding to the next step. If the add-on needs work but is safe to use, it can be given a preliminary review approval without performing any testing. If the add-on needs work and you are not sure if it is safe to use, then leave the add-on for someone else to review, request a admin review, or ask for help in the mailing list.

Step 4: Feature Review

The last step in a review is to install and test the add-on.

Testing setup

These are a few settings and tools you should use or consider using when setting up your add-on testing environment:

  • Always use a separate profile for testing, never your main profile. See Setting up an extension development environment.
  • Ideally you should perform your tests in a virtual machine. It is always useful in case you need to test in multiple platforms. VirtualBox is free and supports most platforms.
  • Enable full Error Console reporting, as described in the Development Preferences section.
  • These add-ons help you inspect add-on behavior and find possible solutions for problems:
    • DOM Inspector. Analyze XUL and HTML layout, CSS and even JS objects.
    • Console2 for detailed Console logging.
    • Tamper Data or Live HTTP Headers for HTTP traffic analysis.
    • Leak Monitor to detect some types of memory leak. See Leak Gauge for a more general solution.
    • Extension Test to detect loose variables and DOM IDs, prototype extension, dangerous category registration, and other difficult to spot problems. Also automatically sets the required dom.report_all_js_exceptions and javascript.options.showInConsole preferences.
  • To test Fennec add-ons, you'll need to install Fennec. It is preferred that you test in a supported mobile device. If a Fennec nomination has been waiting for long, it's OK to test with the desktop XULRunner application.
  • For online malware scanning, you can use Virus Total, Kaspersky online scan and Jotti online scan. AMO performs virus checks, and binary add-ons should be admin-reviewed anyway, but if you suspect anything, those are good tools to use.

Installing and testing

Add-ons are normally cross-platform, so there will only be a single file to review, in the same section where the validator and source links are located. If the add-on is offered for a limited number of platforms, there will be individual links for each one of them. In this case all supported platforms should be tested.

Regarding applications, you don't need to test the add-on for all applications it supports. If the add-on supports Firefox and others, it's OK to only test on Firefox. If, however, an add-on update introduces Fennec or other application support, the add-on should be tested on it. The applications we support for reviews are listed on this page.

Policies and actions

Policy Action Notes
Security violations Reject Adding HTTP content to secure pages. Visit HTTPS sites like and make sure the identity button is unchanged. This is specially important for add-ons that insert scripts into sites.
Identity button
No Surprises violation Preliminary Review Changing homepage, default search provider, including unexpected ads or content changes without explicit user opt-in.
Privacy violations Preliminary Review Incorrect or insufficient privacy policies, not respecting Private Mode.
Errors in the Error Console Preliminary Review
Add-on is very hard to use without instructions Preliminary Review If the add-on is difficult to use, there should be instructions included in the add-on descriptions, or in a startup page or window.
Toolbar buttons are not customizable Preliminary Review
Memory leaks from content or chrome Preliminary Review If an add-on touches the content in any way, we need to test the add-on on a page where it works, close the page, and then look in about:memory?verbose. Remaining compartments related to the page indicate a memory leak. After disabling the add-on (and minimizing memory usage) the add-on should no longer use any memory. If it does, it leaks to chrome. More details here and


Affiliate linking Preliminary Review See details below.
Requires third party software or paid registration Admin Review This excludes add-ons that require other add-ons to function, like Firebug extensions.
Inserts ads into content Admin Review The rules in these cases are complex. They need to be clearly labeled as coming from the add-on (otherwise Prelim). They can't remove or replace existing ads (otherwise Reject). They need to follow No Surprises (otherwise Prelim). And there are also security concerns (Reject) and privacy concerns (Prelim).

Other tests to perform:

  • Visit a very simple website like and inspect its DOM, looking for any changes. Again, this is particularly important for extensions that insert scripts or make DOM changes.
  • Open the add-on's preferences window, from the Add-ons Manager and elsewhere, and verify that preference changes apply properly. Make sure the window fits all of its contents (a common problem in Mac OS).
  • Test all add-on features, within reason. If there too many, focus on the main features.
  • Remove all added toolbar buttons, disable all added toolbars, and restart the browser. Make sure that buttons and toolbars are all removable and do not reappear on restart. Make sure that missing toolbar buttons to not cause errors to appear in the Error Console.
  • Open the Customize Toolbar dialog and make sure that all buttons have appropriate icons and label text.
  • Affiliate linking. Some add-ons add affiliate codes to Amazon links (or similar) in order to make money. At the moment we allow this as long as (1) the add-on follows the No Surprises policy, (2) the feature doesn't replace or remove any existing affiliate codes, (3) the affiliate codes aren't inserted in the merchant website's links (inserting Amazon affiliate codes in pages).

Step 5: Resolution

Choose the appropriate resolution and include all of your notes. Make sure you use a corteous and professional tone, and be as helpful as you can when pointing out problems or areas for improvement. If you are pushing the add-on public, thank the author for the time and effort they have put in. Once you're ready, click the Process Action button.

The submission of the review form can fail for a number of reasons, so it is highly recommended that you copy of your notes to the clipboard before you click on the submit button. You can also use add-ons like Textarea Cache for this.

Editor tour: remember to ask the admin editor to review your response before sending it.

Next: Theme Reviews