WebExtensions support on AMO

It’s been possible to submit WebExtensions add-ons to addons.mozilla.org (AMO) since February, but I wanted to take a moment to highlight some of the improvements we’ve made since then that make it much easier to get your Chrome or Opera add-on into AMO.

These features have all been deployed to AMO over the last couple of months and are available for use.

New linter

We are now using the add-ons linter for WebExtensions which means that when we parse a WebExtensions add-on, we are running through a new JavaScript-powered linter, instead of the Python one. This parsing occurs each time you upload a new add-on or a new version of an add-on.

It uses eslint to parse the JavaScript and a schema to verify that the WebExtensions manifest is correct. Because we’ve started to implement functionality in the new add-ons linter that didn’t exist in the old version, more things will be showing up as warnings.

As an example, if you request a permission in the manifest that Firefox doesn’t support, you’ll get a warning:


Relaxed upload criteria

If you’ve developed and add-on for Chrome or Opera, we’d like you to upload it to AMO. For this reason, we’ve relaxed a few criteria around AMO. Once you’ve verified that an add-on works correctly using about:debugging, you should then be able to upload it to AMO quite easily. We’ve hopefully made this easier through the following steps:

Optional add-on id

If your WebExtension does not have an id specified in the manifest.json, then AMO will generate an id for your add-on and add it to the add-on signing process. You can then get the add-on id from AMO and re-use that in later API calls, if needed.

The command line tool web-ext also supports optional ids.


AMO will now accept an add-on as a zip file or a crx file. It will still only emit xpi files that Firefox and other Mozilla projects can consume. In the case of a crx file, the extra data added by the Chrome store will be stripped out of the file.

We recommend using a tool like web-ext to generate the appropriate file for your add-on.

Comments in the manifest file

Although comments are not valid in a JSON file, Chrome supports comments in the manifest.json file. To keep compatibility with Chrome, the addons-linter and hence AMO now support comments in the manifest file, but only comments starting with a double slash (//).


Finally, AMO now supports translations in the manifest. This again follows the Chrome standard, so that:

//in manifest.json:
"default_locale": "en",
"name": "__MSG_appName__",

//in _locales/en/messages.json:
  "appName": {
    "message": "My Add-on",
    "description": "The name of the add-on."

//in _locales/de/messages.json:
  "appName": {
    "message": "Mein Add-on"

The manifest will be parsed and the translations automatically entered into AMO. You need to ensure that default_locale is set in the manifest for the localisations to be activated. On the first upload, AMO will process the translations:

Screenshot 2016-07-14 09.44.11

If you’d like to get involved then join our mailing list or check out our repositories on Github.

Add-ons Update – Week of 2016/07/13

I post these updates every 3 weeks to inform add-on developers about the status of the review queues, add-on compatibility, and other happenings in the add-ons world.

The Review Queues

In the past 3 weeks, 1278 listed add-ons were reviewed:

  • 1194 (93%) were reviewed in fewer than 5 days.
  • 62 (5%) were reviewed between 5 and 10 days.
  • 22 (2%) were reviewed after more than 10 days.

There are 74 listed add-ons awaiting review.

You can read about the recent improvements in the review queues here.

If you’re an add-on developer and are looking for contribution opportunities, please consider joining us. Add-on reviewers are critical for our success, and can earn cool gear for their work. Visit our wiki page for more information.


The compatibility blog post for Firefox 48 is up, and the bulk validation was run. The post for Firefox 49 is also up and the bulk validation will be run in the coming weeks.

As always, we recommend that you test your add-ons on Beta and Firefox Developer Edition to make sure that they continue to work correctly. End users can install the Add-on Compatibility Reporter to identify and report any add-ons that aren’t working anymore.

Extension Signing

The wiki page on Extension Signing has information about the timeline, as well as responses to some frequently asked questions. The current plan is to remove the signing override preference in Firefox 48. The unbranded builds, which were the final piece, are available here. We will update the Extension Signing doc with more information about how to obtain them.


We would like to thank these people for their recent contributions to the add-ons world: Sylwia Ornatowska, dw-dev, Lavish Aggarwal, Baris Derin, Martin Giger, Viswaprasath, gorf4673, and Atique Ahmed Ziad.

You can read more about their contributions in our recognition page.

July 2016 Featured Add-ons

Firebug console panel view with an example of error logs.

Firebug console panel view with an example of error logs.

Pick of the Month: Firebug

by Firebug Working Group
Access a bevy of development tools while you browse—edit, debug, and monitor CSS, HTML, and JavaScript live in any Web page.

”One of the main reasons why I love Firefox. Cannot imagine Firefox without Firebug.”

Featured: ipFood

by hg9x
Browse the Web anonymously by generating random proxies.

”Everything works perfectly.”

Nominate your favorite add-ons

Featured add-ons are selected by a community board made up of add-on developers, users, and fans. Board members change every six months, so there’s always an opportunity to participate. Stayed tuned to this blog for the next call for applications. Here’s further information on AMO’s featured content policies.

If you’d like to nominate an add-on for featuring, please send it to amo-featured@mozilla.org for the board’s consideration. We welcome you to submit your own add-on!

Mozlondon Debriefer

teamFrom June 13 – 17, more than a thousand Mozillians descended on London to celebrate the accomplishments of the past six months and collaborate on priorities for the latter half of the year. The add-ons team and a handful of volunteers did just that, and we wanted to share some of the highlights.

Add-on reviews

We celebrated the fact that review times have dropped dramatically in 2016. Last year, most add-on submissions got clogged in the review queue for 10 or more days. Now, 95% of submissions are reviewed in under five days (84% in less than 24 hours!). This is a huge boon to our developer community and a great credit to our tireless, mostly-volunteer review team.

Review efficacy should continue to trend positively over the balance of this year. We furthered plans to simplify the review process by eliminating preliminary reviews, among other streamlining initiatives.


It’s likely not a surprise to learn that WebExtensions dominated engineering discussions in London. Here are a few top-level items…

… A WebExtensions Advisory Group has been formed. This cross-disciplinary body is primarily tasked with providing input around the development of future APIs.

… We saw some inspired demos, like runtime.connectNative, which will allow add-ons to communicate out of process; and the auto-reload function for WebExtensions (set to land in 49); plus a demo of a hybrid add-on that allows an SDK add-on to embed a WebExtension add-on, allowing developers to start using the WebExtension API and migrate their users.

… Prioritized future work for WebExtensions was solidified, including permissions support, Chrome parity support for top Chrome content, and end-to-end automated installation testing.

… We recapped many recent WebExtensions advancements, such as the implementation of dozens of new APIs (e.g. history, commands, downloads, webNavigation, etc.)

Community & Editorial

It’s worth recognizing all the diverse ways our community contributes to the success of add-ons—coders, content reviewers, curators, translators, tech writers, evangelists, student ambassadors, and more—our community is integral in providing Firefox users with the power to personalize their Web experience and AMO’s ability to support a massive ecosystem of more than 32,000 extensions and 400,000 themes.

One of the focal points of our community discussions in London was: How can we do more to move volunteers up the contribution curve, so we can nurture the next generation of leaders? What more can we do to turn bug commenters into bug fixers, developers into evangelists, and so forth? Check out the notes from this session and add your ideas there!

On the editorial side, we started exploring ways of re-thinking content discovery. Of course we have the AMO site as a content discovery destination with more than 15 million monthly users, but research tells us the majority of Firefox users hardly know what an add-on is, let alone where to find one. So how can we introduce the wonder of add-ons to a broader Firefox audience?

A general consensus emerged—we need to take the content to where the user is, to key moments in their everyday Web experience where perhaps an add-on can address a need. This is just one of the projects we’ll begin tackling in the second half of the year. If you’d like to get involved, you’re invited to join our weekly public UX meeting.

To get involved with the add-ons world, please visit our wiki page, or get in touch with us at irc.mozilla.org in the #addons channel.

Add-on Compatibility for Firefox 49

Firefox 49 will be released on September 13th. Here’s the list of changes that went into this version that can affect add-on compatibility. There is more information available in Firefox 49 for Developers, so you should also give it a look.


XPCOM and Modules

Let me know in the comments if there’s anything missing or incorrect on these lists. If your add-on breaks on Firefox 49, I’d like to know.

The automatic compatibility validation and upgrade for add-ons on AMO will happen in a few weeks, so keep an eye on your email if you have an add-on listed on our site with its compatibility set to Firefox 48.

Friend of Add-ons: Yuki Hiroshi

piro-photoPlease meet our newest Friend of Add-ons: Yuki “Piro” Hiroshi. A longtime add-on developer with 37 extensions and counting (he’s most proud of Tree Style Tab and Second Search), Hiroshi also recently filed more than two dozen high-impact WebExensions bugs.

Hiroshi recently recounted his experience porting one of his XUL add-ons to WebExtensions in the hopes that he could help support fellow add-on developers through the transition. He likens XUL to an “experimental laboratory” that over the past decade allowed us to explore the possibilities of a customized web browser. But now, Hiroshi says, we need to “go for better security and stability” and embrace forward-thinking API’s that will cater to building richer user experiences.

While add-ons technology is evolving, Hiroshi’s motivation to create remains the same. “It’s an emotional reason,” he says, which took root when he first discovered the power of a Gecko engine that allowed him to transform himself from being a mere hobbyist to a true developer. “Mozilla is a symbol of liberty for me,” Hiroshi explains. “It’s one of the legends of the early days of the web.”

When he’s not authoring add-ons, Hiroshi enjoys reading science fiction and manga. A recent favorite is The Hyakumanjo Labyrinth, a “bizarre adventure story” that takes place on an infinity field beyond space and time within an old Japanese apartment building.

Do you contribute to AMO in some fashion? If so, don’t forget to add your contributions to our Recognition page!

Add-ons Update – Week of 2016/06/22

I post these updates every 3 weeks to inform add-on developers about the status of the review queues, add-on compatibility, and other happenings in the add-ons world.

The Review Queues

In the past 3 weeks, 1432 listed add-ons were reviewed:

  • 1354 (95%) were reviewed in fewer than 5 days.
  • 45 (3%) were reviewed between 5 and 10 days.
  • 33 (2%) were reviewed after more than 10 days.

There are 61 listed add-ons awaiting review.

You can read about the recent improvements in the review queues here.

If you’re an add-on developer and are looking for contribution opportunities, please consider joining us. Add-on reviewers get invited to Mozilla events and earn cool gear with their work. Visit our wiki page for more information.

Compatibility Communications

Most of you should have received an email from us about the future compatibility of your add-ons. You can use the compatibility tool to enter your add-on ID and get some info on what we think is the best path forward for your add-on. This tool only works for listed add-ons.

To ensure long-term compatibility, we suggest you start looking into WebExtensions, or use the Add-ons SDK and try to stick to the high-level APIs. There are many XUL add-ons that require APIs that aren’t available in either of these options, which is why we ran a survey so we know which APIs we should look into adding to WebExtensions. You can read about the survey results here.

We’re holding regular office hours for Multiprocess Firefox compatibility, to help you work on your add-ons, so please drop in on Tuesdays and chat with us!

Firefox 48 Compatibility

The compatibility blog post for Firefox 48 is up, and the bulk validation will be run shortly.

As always, we recommend that you test your add-ons on Beta and Firefox Developer Edition to make sure that they continue to work correctly. End users can install the Add-on Compatibility Reporter to identify and report any add-ons that aren’t working anymore.

Extension Signing

The wiki page on Extension Signing has information about the timeline, as well as responses to some frequently asked questions. The current plan is to remove the signing override preference in Firefox 48.

Multi-process Firefox and AMO

In Firefox 48, which reaches the release channel on August 1, 2016, multi-process support (code name “Electrolysis”, or “e10s”) will begin rolling out to Firefox users without any add-ons installed.

In preparation for the wider roll-out to users with add-ons installed, we have implemented compatibility checks on all add-ons uploaded to addons.mozilla.org (AMO).

There are currently three possible states:

  1. The add-on is a WebExtension and hence compatible.
  2. The add-on has marked itself in the install.rdf as multi-process compatible.
  3. The add-on has not marked itself compatible, so the state is currently unknown.

If a new add-on or a new version of an old add-on is not multi-process compatible, a warning will be shown in the validation step. Here is an example:


In future releases, this warning might become more severe as the feature nears full deployment.

For add-ons that fall into the third category, we might implement a more detailed check in a future release, to provide developers with more insight into the “unknown” state.

After an add-on is uploaded, the state is shown in the Developer Hub. Here is an example:


Once you verify that your add-on is compatible, be sure to mark it as such and upload a new version to AMO. There is documentation on MDN on how to test and mark your add-on.

If your add-on is not compatible, please head to our resource center where you will find information on how to update it and where to get help. We’re here to support you!

WebExtensions for Firefox 49

Firefox 49 landed in Developer Edition this week, so we have another update on WebExtensions for you!

Since the release of Firefox 48, we feel WebExtensions are in a stable state. We recommend developers start to use the WebExtensions API for their add-on development. Since the last release, more than 35 bugs were closed on WebExtensions alone.

If you have authored an add-on in the past and are curious about how it’s affected by the upcoming changes, please use this lookup tool. There is also a wiki page and MDN articles filled with resources to support you through the changes.

APIs Implemented

The history API allows you to interact with the browser history. In Firefox 49 the APIs to add, query, and delete browser history have been merged. This is ideal for developers who want to build add-ons to manage user privacy.

In Firefox 48, Android support was merged, and in Firefox 49 support for some of the native elements has started to land. Firefox 49 on Android supports some of the pageAction APIs. This work lays the foundation for new APIs such as tabs, windows, browserAction in Android.

The WebNavigation API now supports the manual_subframe transitionType and keeps track of user interaction with the url bar appropriately. The downloads API now lets you download a blob created in a background script.

For a full list of bugs, please check out Bugzilla.

In progress

Things are a little bit quieter recently because there are things in progress that have absorbed a lot of developer time. They won’t land in the tree for Firefox 49, but we’ll keep you updated on their progress in later releases.


This API allows you to store some data for an add-on in Firefox and have it synced to another Firefox browser. It is most commonly used for storing add-on preferences, because it is not designed to be a robust data storage and syncing tool. For sync, we will use Firefox Accounts to authenticate users and enforce quota limits.

Whilst the API contains the word “sync” and it uses Firefox Accounts, it should be noted that it is different from Firefox Sync. In Firefox Sync there is an attempt to merge data and resolve conflicts. There is no similar logic in this API.

You can track the progress of storage.sync in Bugzilla.


This API allows you to communicate with other processes on the host’s operating system. It’s a commonly used API for password managers and security software which needs to communicate with external processes.

To communicate with a native process, there’s a two-step process. First, your installer needs to install a JSON manifest file at an appropriate file location on the target computer. That JSON manifest provides the link between Firefox and the process. Secondly, the user installs the add-on. Then the add-on can call the connectNative, sendNativeMessage and other APIs:

  { text: "Hello" },
  function(response) {
    console.log("Received " + response);

Firefox will start the process if it hasn’t started already, and pipe commands through to the process. Follow along with the progress of runtime.connectNative on Bugzilla.

WebExtensions transition

With these ongoing improvements, we realise there are lots of add-ons that might want to start moving towards WebExtensions and utilise the new APIs.

To allow this, you will soon be able to embed a WebExtension inside an add-on. This allows you to message the WebExtension add-on.

The following example works with SDK add-ons, but this should work with any bootstrapped add-on. Inside your SDK add-on you’d have a directory called webextensions containing a full-fledged WebExtension. In the background page of that WebExtension will be the following:

chrome.runtime.sendMessage("test message", (reply) => {
  console.log("embedded webext got a reply", reply);

Then you’d be able to reply in the SDK add-on:

var { api } = require('sdk/webextension');
api.onMessage.addListener((msg, sender, sendReply) =>
  console.log("SDK add-on got a message", {msg,sender}); 

This demonstrates sending a message from the WebExtension to the SDK add-on.Persistent bi-directional ports will also be available.

Using this technique, we hope add-on developers can leverage WebExtensions APIs as they start migrating their add-on over to WebExtensions. Follow along with the progress of communication on Bugzilla.

There are also lots of other ways to get involved with WebExtensions, so please check them out!

Developer profile: Luís Miguel (aka Quicksaver)

Luís Miguel claims to "bleed" add-ons.

“I bleed add-on code,” says Luís Miguel.

Always a heavy user of bookmarks and feeds, Luís Miguel one day decided to customize his Firefox sidebar to better accommodate his personal tastes (he didn’t like how the ever-present sidebar pushed web content aside). But Luís soon discovered he could only go so far solving this problem with minor CSS tweaks.

That’s when he resolved himself to develop a full-blown add-on. He created OmniSidebar, an elegant extension that allows you to slide your sidebar into view with a simple gesture, among other rich interface features.

Another of Luís’ add-ons—FindBar Tweak—has a similar origin story; Luís identified a personal desire first, then built an add-on to address it. In this case he wanted a quick way to scan code for just the parts applicable to his work.

“Earlier today I was working with pinned tabs, and I had to research how they happen,” explains Luís. “Looking for the word ‘pinned’ in Firefox’s code using FindBar Tweak, I was able to easily read through only the relevant bits in a few seconds, because it not only takes me directly to what I’m looking for, but also helps me visually make sense of what is actually relevant.”

Luís has created four other add-ons, including the popular Tab Groups. Luís spoke with me briefly about his unique interest in add-ons…

It sounds like you basically create all of your add-ons based on personal browsing needs. Is that an accurate characterization?
Luís Miguel: Yeah, that’s a fair way to put it. Everything has been about making my Firefox behave and interact with me the way I prefer it to, from quickly finding what I’m looking for in a page, to having my feeds and bookmarks readily accessible without screwing up the rest of the page layout, properly organizing all my buttons in the browser, keeping a clean window but always ready to interact in whatever way I need it to. The “anything goes” approach of Firefox add-ons make them a very fun playground for me in that respect.

As a procrastination enthusiast, I’ve found that when the process—towards whatever goal—is optimal, fast, and effective, I am the most motivated to do it. So I look for every way to enhance productivity in every task I do, not just for developing, even just casual browsing really.

Puzzle Bars can conveniently pull up your customized toolbar with a simple swing of the mouse.

Puzzle Bars conveniently pulls up your customized toolbar with a simple swing of the mouse.

Although, that’s not entirely the case anymore. There’s a lot in my add-ons that come from user suggestions and requests, many [features] I don’t really use myself. But if it’s to improve the add-on and I have the availability to do it, how can I say no to the most awesome and supportive users a developer could ask for?

Beyond add-ons you’ve created, do you do other types of development?
LM: I’ve contributed a few patches for Firefox itself through Bugzilla, but that’s about it. When I set out to do something, I focus on it, so right now I bleed add-on code.

Are you working on any new add-ons you want to tell us about? 
LM: I do have a couple of ideas for new add-ons, but those probably won’t happen for a while, mostly because I have to focus on my current ones a lot, as they will need to be ported to WebExtensions eventually. Since my add-ons are mostly UI-modifications at their base, that will be… challenging.

I have been working on Tab Groups 2 though, which is a major rewrite of almost everything, to hopefully make it more stable and perform better. It’s turning out really awesome.

What other add-ons—ones you haven’t created—are your favorites and why?
LM: I have around 30 add-ons enabled in my main profile at any one time. A few favorites come to mind…

AdBlock Plus is always at the top of my list. I dislike waiting a long time for pages to fully load because of several blinking boxes, or misleading ads.

Download Panel Tweaker for a sleek, direct, and fully functional downloads panel.

Tab Mix Plus for optimized opening, closing, moving, and loading tab behavior. There’s just so much it can do!

Stylish for a few nits here and there, and the custom glass style I made for myself, which I’ve found no other theme or add-on out there can even come close to this.

I especially like Turn Off the Lights. It helps me focus on whatever video I’m watching. I tend to get distracted easily. If there’s something in the corner of my eye that stands out for some reason, I will look at it. So that functionality is simple and yet very effective.

Thanks for chatting with us, Luís! I can think of no better way to close this conversation than by sharing a recent installment of your web series…