Friend of Add-ons: Trishul Goel

Our newest Friend of Add-ons is Trishul Goel! Trishul first became involved with Mozilla five years when he was introduced to the Firefox OS smartphone. As a JavaScript developer with an interest in Mozilla’s mission, he looked for opportunities to get involved and began contributing to SUMO, L10n, and the Firefox OS Marketplace, where he contributed code and developed and reviewed apps.

After Firefox OS was discontinued as a commercial product, Trishul became interested in contributing to Mozilla’s add-ons projects. After landing his first code contributions to (AMO), he set about learning how to develop extensions for Firefox using WebExtensions APIs. Soon, he began sharing his knowledge by leading and mentoring  workshops for extension developers as part of Mozilla’s “Build Your Own Extension” Activate campaign.

In the last year, Trishul has contributed more than 45 patches to Mozilla’s add-ons repositories, published 11 extensions to AMO, served as a member of the Featured Add-ons Advisory Board, and created a great set of WebExtensions APIs tutorials for new extension developers. Currently, he is an active Mozilla Rep and Tech Speaker, and is writing React code for AMO.

When asked what he has gained from his experience contributing to Mozilla, Trishul says, “I grew my skill set while coding for Mozilla. I’ve learned how to mentor people and how to work on a cross-culture remote team.”

In his free time, Trishul enjoys traveling and mountain biking.

Congratulations, Trishul, and thank you for your contributions to the add-ons community!

Are you a contributor to the add-ons community or know of someone who should be recognized? Please be sure to add them to our Recognition Wiki!

New Contribution Opportunity: Content Review for

For over a dozen years, extension developers have volunteered their time and skills to review extensions submitted to (AMO). While they primarily focused on ensuring that an extension’s code adhered to Mozilla’s add-on policies, they also moderated the content of the listings themselves, like titles, descriptions, and user reviews.

To help add-on reviewers focus on the technical aspects of extension review and expand contribution opportunities to non-technical volunteers, we are creating a new volunteer program for reviewing listing content.

Add-on content reviewers will be focused on ensuring that extensions listed on AMO comply with Mozilla’s Acceptable Use Policy. Having a team of dedicated content reviewers will help ensure that extensions listed on AMO are not spam do not contain hate speech or obscene materials.

Since no previous development experience is necessary to review listing content, this is a great way to make an impactful, non-technical contribution to AMO. If you have a keen eye for details and want to make sure that users and developers have a great experience on, please take a look at our wiki to learn more about how to become an add-on content reviewer.

January’s Featured Extensions

Firefox Logo on blue background

Pick of the Month: Search by Image – Reverse Image Search

by Armin Sebastian
Powerful image search tool that’s capable of leveraging multiple engines, such as Google, Bing, Yandex, Baidu, and TinEye.

“I tried several ‘search by image’ add-ons and this one seems to be the best out there with a lot of features.”

Featured: Resurrect Pages

by Anthony Lieuallen
Bring back broken links and dead pages from previous internet lives!

“One of my favorite websites took down content from readers and I thought I’d never see those pages again. Three minutes and an add-on later I’m viewing everything as if it was never deleted. Seriously stunned and incredibly happy.”

Featured: VivaldiFox

by Tim Nguyen
Change the colors of Firefox pages with this adaptive interface design feature (akin to Vivaldi-style coloring).

“Definitely brings a bit more life to Firefox.”

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. 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 [at] mozilla [dot] org for the board’s consideration. We welcome you to submit your own add-on!

December’s Featured Extensions

Firefox Logo on blue background

Pick of the Month: Group Speed Dial

by Juraj
Organize all your favorite websites with visual bookmarks.

“Fast. All other speed dials are resource hungry and slow.”

Featured: Gesturefy

by Robbendebiene, Itch
Enjoy 40+ customizable mouse gestures. Includes multi-language support.

“Very good as an alternative to FireGesture.”

Featured: Tree Style Tab

by Piro
Display your open tabs in a tree style.

“Perfect for opening lots of tabs on a widescreen monitor. All tabs remain readable contrary to the normal tab layout.”

Featured: Multi-Account Containers

by Mozilla
An official Mozilla extension, Multi-Account Containers lets you keep distinct parts of your online life separated into color-coded tabs. Cookies are separated by container, allowing you to use the Web with multiple identities simultaneously.

“This add-on is my daily partner. Now Facebook doesn’t know what I buy ;).”

Featured: User-Agent Switcher

by RayLo
A tool to spoof user-agent strings.

“Easy to use and portable too. Thank you!!”

Featured: Tab Auto Refresh

by Alex
Automatically refresh your tabs on custom time intervals.

“This is the first auto reload/refresh Firefox extension that I’ve found that can be customized for each tab that I have! This is exactly what I wanted and it works fantastic. Highly recommended.”

Featured: Google Translator

by Andy Portman
Access a simple way to translate single words or large, complex phrases.

“Easy to use, amazing pop-up background, a powerful dictionary translator!”

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. 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 [at] mozilla [dot] org for the board’s consideration. We welcome you to submit your own add-on!

Extensions in Firefox 58

With the release of Firefox Quantum on November 14, 2017, we officially entered a WebExtensions-only world for add-on development. While that event was certainly the news of the day, Firefox 58 quietly entered Beta and a host of new APIs and improvements landed. As always, documentation for the APIs discussed here can be found on MDN Web Docs.

Additional Theme API

The API around themes continues to grow, allowing you customize even more of the browser appearance. In Firefox 58, you can now:

Reader Mode API Added to Tabs

The API available for interacting with tabs continues to grow. Firefox reader view (or reader mode) strips away clutter like buttons, ads and background images, and changes the page’s text size, contrast, and layout for better readability. It can even read the page out loud to you, if you want.

The image below shows a page that can be viewed in reader mode, indicated by the page icon in the URL bar (circled in red).

MDN article in Normal Mode.Clicking on the icon puts the page in reader mode, removing most of the page elements except the text and adding buttons to the left-hand side that modify the reading experience.

MDN article in Reader Mode.This powerful browser feature is now available via the WebExtensions API.

Improved webRequest API

Extensions can now easily get the entire URL ancestor chain, even in an HTTP environment. webRequest.onBeforeRequest() now includes another parameter in its callback object called frameAncestors. This is an array that contains information for each document in the frame hierarchy up to the top-level document.

Additionally, to enable proxy authorization to work smoothly,  webRequest.onAuthRequired() now fires for system events. If an extension has the correct permissions, it will be able to use onAuthRequired to supply credentials for proxy authorization.

Flexible XHR and Fetch Headers

When a content script makes requests using the standard window.XMLHttpRequest or window.fetch() API, the Origin and Referer headers are not set like they would be when requests come from the web page itself. This is often desirable in a cross-domain situation so that the content script does not appear to come from a different domain.

However, some sites only allow XHR and fetch to retrieve content if the correct Referer and Origin headers are set. Starting in Firefox 58, the WebExtensions API permits the use of content.XMLHttpRequest() and content.fetch() to perform requests that look as if they were sent by the web page content itself.

Improved Content Security Policy (CSP) Handling

Work also continues in the WebExtensions CSP area. Starting with Firefox 58, the CSP of a web page does not apply to content inserted by an extension. This allows, for example, the extension to load its own resources into a page.

This is a fairly large effort requiring some substantial architectural work. In Firefox 58, the first part of this work has landed, permitting basic injection of content generated by DOM APIs. There will be follow-ups for parser-generated content and inline stylesheets and scripts.

Setting the Default Search Engine

Using chrome_settings_override, an extension can now install a new default search engine by setting the is_default key to TRUE.  To protect the user, this cannot be done silently and the user will see an additional dialog that prompts them to confirm the change.

Search Engine ConfirmationThe user will also see if their default search engine has been overridden in the Options (about:preferences) page, which is explained in more detail below.

User Notification of Extensions Overrides

As the scope and power of the WebExtensions API increases, it is important to maintain the user’s security and privacy. In addition to the permission dialog that a user sees upon installation, Firefox tries to make sure that users are aware of which parts of the browser are under the control of an extension, and provide a way for them to revert back to default behavior, if desired.

Firefox 58 landed a couple of features in this area. First, when an extension has taken control of the New Tab Page, a notice is shown in Options (about:preferences) along with a button to disable the extension.  This is shown in the screenshot below.

Extension OverridesAlong similar lines, if an extension has set a user’s default search engine, this will be shown on the Options (about:preferences) page.

Extension OverridesOver the next few releases expect to see Firefox show even more areas where an extension is in control of a browser behavior along with options to revert back to a default state.

Additional Privacy Controls

In keeping with Mozilla’s mission to protect an individual’s online security and privacy, two new browser settings related to user privacy are now exposed via the WebExtensions API.  Within privacy.websites, we’ve added:

  • firstPartyIsolate – This preference makes the browser associate all data (including cookies, HSTS data, cached images, and more) for any third party domains with the domain in the address bar.
  • resistFingerprinting – Browser fingerprinting is the practice by which websites collect data associated with the browser or the device it’s running on to personally identify you. This preference makes the browser report spoofed information for data that’s commonly used for fingerprinting.

Browser Action Fixes

A number of changes landed in Firefox 58 that fix issues with Browser Action buttons:

Support for PKCS #11 Security Devices

Firefox supports manual installation of external security devices via a dialog under the Options (about:preferences) screen. Now, WebExtensions includes API support for PKCS #11 security devices. Similar to native messaging and managed storage, a native manifest must be installed outside of an extension before the API become useful.


On Android, users get install-time prompts for WebExtension permissions, but under Firefox 58 they now also get prompts when an extension adds additional permissions at runtime.

Miscellaneous Changes

More to Come

The items above represent some of the bigger changes, but Firefox 58 landed a total of 79 items in the WebExtensions area. Thank you to everyone who had a part in getting Firefox 58 to Beta, especially volunteer contributors apoorvasingh2811, DW-dev, Tom Schuster, Kevin Jones, Ian Moody, Tim Nguyen, Tomislav Jovanovic, Masatoshi Kimura, Wouter Verhelst.

We continue to receive a lot of feedback from developers and, based on that feedback, work is progressing on new features for Firefox 59 and beyond. Expect to see the WebExtensions API improve and grow, particularly in regards to the organization and management of tabs, as well as the theming API. As always, thank you for using Firefox and helping ensure that individuals have the ability to shape the Internet and their own experiences on it.

Q&A with Developer Stefan Van Damme

This is a guest post from Mozilla technical writer Judy DeMocker. She recently chatted with Stefan Van Damme about his extension Turn Off the Lights, and his experience porting it from its original Google Chrome version. Take it away, Judy…

Stefan Van Damme had a small problem—but it happened all the time. He liked to watch videos online, but video players on sites like YouTube don’t eliminate the other content on the screen—and that makes it hard to focus on the show. So Stefan, who lives in Antwerp, Belgium, built his first browser add-on to dim the lights on distracting content. And since so many people love movies, he built it for seven different browsers for users around the world.

Stefan’s extension, Turn Off the Lights, has been downloaded more than 3 million times. With that many users, it’s critical for him to be able to update it quickly and easily, without spending days or weeks on maintenance. So he’s excited about the new WebExtensions API, which makes it easy for him to port his extensions to Google Chrome, Mozilla Firefox, and Microsoft Edge using a universal code base.

Turn Off the Lights in action.


Porting to Firefox

What browser did you first create your extension for?
Google Chrome

Why was it important for you to write your extension for Firefox?
It is important to me that everyone can have the Turn Off the Lights experience in their favorite web browser. And Firefox is still one of the most popular web browsers out there today.

Did you migrate your add-on from the legacy Firefox platform, XUL? How difficult was that?
In the first version of Turn Off the Lights, I used the XUL technology. If I had to migrate to the new version, it would be difficult. However, I already had the Chrome extension, so migrating that code to Firefox was very easy. There was only one file I had to change, the manifest file. All the other files, I had to do nothing.

How difficult was it to learn and write to the WebExtensions API? (1 = easiest; 10 = hardest)
Since Firefox now supports the WebExtensions API, it was very easy to take code that runs on Chrome or Edge and put it on Firefox. I can use the same code base and just change the settings to work with each browser. If I continue with Chrome extensions, then it’s just a “1,” very easy.

Did you find all the functionality of your XUL add-on in the WebExtensions API? Or did you have to learn a new way to write the same features?
At the time I wrote the XUL add-on from my Chrome extension code, it was difficult, but I got all the functions inside. Today WebExtensions have more APIs, even those that extend outside the website content. For example, the extension can now dim the toolbar of Firefox thanks to the browser.theme API. And that is very unique and also cool.

What problems, if any, did you experience developing for Firefox?
Mostly I had trouble with the performance of the browser. If I click on my gray lamp button, it goes very slowly to that capacity level. On other browsers, it’s one click and done. I understand Mozilla is working hard to improve this.

What do you think of the new Quantum version of Firefox?
I see some good improvement in the Firefox Quantum web browser. That is what I like, and it can also be good for my users.

Tools & Resources

How has the technology changed since 2009?
At first, I used Notepad ++ on Windows to write my code. Now I use a Mac and Microsoft Visual Studio. Visual Studio is a better experience for both platforms. I can use it on Mac and Windows (using Boot Camp). I can switch to a Windows PC and use the same developer kit to write code and test it also.

How long does it take to publish a Firefox extension?
It’s very quick to publish an update to an add-on. Normally I just zip it and click on “Publish” and it’s done. Yesterday, I updated my Date Today add-on, and it took 10 to 15 minutes.

How is adoption of your new extension?
It’s good. Turn Off the Lights has been downloaded more than 3,000,000 times. I’’ve set up my website to detect a visitor’s browser and send them to the correct hyperlink, so they can download the version that works for them.

How long does it take up update your different extensions?
So in browsers like Chrome, Firefox, and Opera, it takes about two hours to update my add-on. I do one or two major updates for Turn Off the Lights a year, for instance moving from version 3.3 to 3.4. Those take more time. But it’s worth it. I get user feedback from my users that those updates provides better harmony in the current web experience.

What resources helped you learn about the WebExtensions API?
The MDN website was helpful. I was working with the Chrome documentation, but their site only shows information for the Chrome platform. That’s a minus for the Google team. They didn’t have a browser compatibility table that could show me if a feature is available on another web browser.

What help, if any, did you get from Mozilla?
I didn’t talk to anybody at Mozilla. But I do report bugs and performance issues. It’s important to get a great experience on all web browsers.

What advice would you give other developers who are thinking of creating extensions for Firefox?
Just do it. And, listen to your users’ feedback. They are the experts on how you can improve your Firefox extension.

Related content

Q&A with Grammarly’s Sergey Yavnyi

Why I Switched from Chrome to Firefox Quantum

Porting a Google Chrome Extension

Cross-browser extensions, available now in Firefox

Remaking Lightbeam as a Browser Extension

Keeping Tabs on the Tab API

tabsTabs are central to the modern browsing experience, so much so that it is hard to imagine that we once browsed the Internet without them, one single window at a time. Now, it’s common to have several tabs open at once — perhaps one playing music, several with online articles you want to read later (pro tip: check out Pocket for this use case), and of course, a few tabs with whatever you are supposed to be working on at the moment.

The Past

From the start, Firefox extensions that dealt with tabs were a natural fit and have proven to be quite popular. The good news is that there are already hundreds of extensions written with the WebExtensions API to help you configure, organize and otherwise manage your browser tabs. You can arrange your tabs as tiles or in a tree, put them on the side of the browser, or control where new tabs open, just to name a few.

Unfortunately, not every feature that was available in the past can be offered using the WebExtensions API. Several of the most popular tab extensions under the legacy add-on system used the unrestricted nature of that environment to offer powerful and unique features. Along with that power, however, came security risks. The WebExtensions API seeks to temper those risks by providing limited access to browser internals.

The Future

We’re working to support additional tab features, but how we achieve this goal will be shaped by our dedication to Web standards, the speed and stability of Firefox, our product vision, and especially our commitment to security and privacy and the principles of the Manifesto. It’s clear that some previously available tab features will not be available under the WebExtensions API; they just can’t be accommodated without potentially compromising user security or privacy.

However, we believe many other features can be added. Providing as much tab-related functionality as we can within these constraints is a high priority. Starting with tab hiding, you can expect to see additional functions added to the WebExtensions API over the next several releases that will allow developers to create rich, compelling extensions to style, manage and organize browser tabs.

All of this, of course, will be part of our push for open Web standards. However, while that process proceeds at its own pace, don’t expect to see us stand still. Using feedback from developers, we will continue to innovate within the WebExtensions API, providing new ways to surprise and delight users. As always, thank you for using Firefox and helping ensure that individuals have the ability to shape the Internet and their own experiences on it.

November’s Featured Extensions

Firefox Logo on blue background

Pick of the Month: User-Agent Switcher (revived)

by Linder
Quickly and easily change your user-agent. There are 26 options to choose from, including iOS, Android, and most common desktop browsers.

“Very simple. Very good.”

Featured: YouTube Video and Audio Downloader

by RayLo
Extremely simple yet powerful video and audio downloader.

“This is the last YouTube downloader you will try, there is no need to continue searching.”

Featured: Mute Tab

by Kelvin_b
Mute all open tabs with a single click.

“I love that all my tabs are automatically muted, as I often click several videos at once.”

Featured: Toolbox for Google Play Store

by Android Police
Adds helpful app browsing features like APKMirror, Android Police, and Appbrain to all Google Play store pages.

“Love it.”

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. 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 [at] mozilla [dot] org for the board’s consideration. We welcome you to submit your own add-on!

What YouTube Downloader is Right for You?

Are you interested in downloading video content? Low resolution or high? Full HD? Or maybe you only want the audio track? How about screengrabs? Perhaps you want all of that and more. Video downloaders are one of the most popular types of extensions for Firefox because there are so many unique ways to handle rich media.

In this post we’ll focus solely on YouTube downloaders, because there’s simply a lot to explore just within the world of video downloaders tailored for YouTube. However, if your video downloading needs aren’t specific to YouTube, I should point out there’s a vast array of video downloaders made for Firefox. The open-source developer community really cranks out some beautiful stuff—everything from do-it-all video downloaders like Video DownloadHelper, Bulk Media Downloader, Video Downloader Professional, Flash and Video Downloader, 1-Click Downloader, and to super niche video downloaders like Instagram Video Download or Private Video Downloader.

Downloading video and audio files is just a couple clicks away with Easy YouTube Downloader Express.

Easy YouTube Downloader Express

If you’re looking for a really solid YouTube downloader that covers the basics and covers them well, check out Easy YouTube Downloader Express. For one, it’s optimized to play well with the new YouTube interface (the new-look YouTube is known to cause problems for some extensions). Easy YouTube Downloader Express also offers 1080p full-HD downloads and handles MP3’s at 256Kbps. Just hit the “Download As:” button that appears conveniently on each video page and select your download preference.

YouTube Video and Audio Downloader

I like the elegance of this YouTube downloader’s interface. Hit a button on any video page and a menu pops up to offer “Quick Download” action or access to a “Download Panel” that displays various resolution and media options. This is a very simple and to-the-point YouTube downloader.

YouTube Video and Audio Downloader displays intuitive controls.

YouTube Download & Adblocker Smarttube

Have you ever eaten Indian pizza? Where they take traditional pizza dough but instead of topping it with stuff like cheese and pepperoni they cook it with curry, masala sauces and other delicious Indian flavors? You eat it and you’re like “why didn’t someone think of this years ago?”

YouTube Download & Adblocker is like that. It’s a great video downloader (that can also handle audio file conversions with an array of formats) PLUS it’s an effective YouTube ad blocker. Genius.

A couple more nice features: you can choose to block annotations with the flick of a checkbox. And with the ad blocker, you have the option to whitelist YouTube channels so ads only appear when you view your favorite content creators.

YouTube Video Download & Convert

If you want gobs of download options, YouTube Video Download & Convert has options—high and low res, static images, audio, even subtitles. It’s also a powerful media converter. All available actions appear as buttons just below the video player, which makes everything super convenient if you don’t mind YouTube pages loaded with buttons.

Easy YouTube MP3

Are you solely interested in converting a YouTube video into an audio MP3 file? That’s all Easy YouTube MP3 does. Quick and painless.

The extensions mentioned above are my favorites (I should probably add Download YouTube Video as well; it’s a really strong video downloader, but some might object to the edgy ads displayed on its custom download page). Did I miss your favorite YouTube downloader? If so please drop suggestions in the comments.

Helping You Find Compatible Extensions

We are getting lots of support requests for finding replacement extensions in the comments section. We can provide better support for this in the forums, so we are shutting off comments here. This thread is where you can see what the community has already suggested, as well as post your own support request.

If you’re a Firefox 57 user (aka Firefox Quantum, released November 14) with legacy extensions installed, there is a feature to help you find compatible replacements.

In the Add-ons Manager (Tools menu > Add-ons), click on “Show legacy extensions” to see a list of your incompatible extensions.

Click on “Find a Replacement”, and you will be taken to the AMO page of a compatible alternative.

If an exact replacement hasn’t been identified, you will land on the Featured Extensions collection, which lists only compatible extensions.

For legacy tab extensions that couldn’t migrate at this time because of unavailable APIs (some of which are being developed and prioritized for release in the coming months), the “Find a Replacement” button directs you to a curated collection of compatible tab extensions.

Not Too Late to Migrate

For developers of legacy extensions who may be in the process of migrating, or have plans to do so in the future, please note that once your extension is compatible, your users will no longer be prompted to find a replacement, and your current users will automatically get the updated version.

So you may still want to update to the WebExtensions API, even if you didn’t get it done in time for Firefox 57. For more information on how to migrate legacy extensions, please see this guide.

If You Need Them a While Longer

We understand that some of you won’t be able to find replacements for your legacy extensions. If you want to use them a while longer while you wait to see if they will be updated by their developers, your best option is Firefox ESR 52. This release is updated for security only, and should work with legacy extensions until the release of Firefox 59, which will also update the ESR release to Quantum.