Add-on Policies Update: Newtab and Search


As part of our ongoing work to make add-ons safer for Firefox users, we are updating our Add-on Policies to add clarification and guidance for developers regarding data collection. The following is a summary of the changes, which will go into effect on December 2, 2019.

  • Search functionality provided or loaded by the add-on must not collect search terms or intercept searches that are going to a third-party search provider.
  • If the collection of visited URLs or user search terms is required for the add-on to work, the user must provide affirmative consent (i.e., explicit opt-in from the user) at first-run, since that information can contain personal information. For more information on how to create a data collection consent dialog, refer to our best practices.
  • Add-ons must not load or redirect to a remote new tab page. The new tab page must be contained within the add-on.

You can preview the policies and ensure your extensions abide by them to avoid any disruption. If you have questions about these updated policies or would like to provide feedback, please post to this forum thread.

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Add-on Policy and Process Updates


As part of our ongoing work to make add-ons safer for Firefox users, we are updating our Add-on Policy to help us respond faster to reports of malicious extensions. The following is a summary of the changes, which will go into effect on June 10, 2019.

  • We will no longer accept extensions that contain obfuscated code. We will continue to allow minified, concatenated, or otherwise machine-generated code as long as the source code is included. If your extension is using obfuscated code, it is essential to submit a new version by June 10th that removes it to avoid having it rejected or blocked.

We will also be clarifying our blocking process. Add-on or extension blocking (sometimes referred to as “blocklisting”), is a method for disabling extensions or other third-party software that has already been installed by Firefox users.

  • We will be blocking extensions more proactively if they are found to be in violation of our policies. We will be casting a wider net, and will err on the side of user security when determining whether or not to block.
  • We will continue to block extensions for intentionally violating our policies, critical security vulnerabilities, and will also act on extensions compromising user privacy or circumventing user consent or control.

You can preview the policy and blocking process documents and ensure your extensions abide by them to avoid any disruption. If you have questions about these updated policies or would like to provide feedback, please post to this forum thread.

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Firefox, Chrome and the Future of Trustworthy Extensions


Browser extensions are wonderful. Nearly every day I come across a new Firefox extension that customizes my browser in some creative way I’d never even considered. Some provide amusement for a short time, while others have become indispensable to my work and life. Extensions are a real-world manifestation of one of Mozilla’s core principles — that individuals must have the ability to shape the internet and their experiences on it.

Another of Mozilla’s core principles is that an individual’s security and privacy on the internet are fundamental and must not be treated as optional. We’ve made the decision to support extensions, but it is definitely a balancing act. Our users’ freedom to customize their browser – their “user agent” – and to personalize their experience on the web can also be exploited by malicious actors to compromise users’ security and privacy.

At Mozilla, we continually strive to honor both principles. It’s why Firefox extensions written to the WebExtensions API are limited in their abilities and have good oversight, including automatic and manual review. It’s also why we make sure users can understand exactly what permissions they’ve granted to those extensions and what parts of their browser they can access.

In short, Mozilla makes every effort to ensure that the extensions we offer are trustworthy.

So it was with great interest that I read Google’s recent Chromium Blog blog post entitled “Trustworthy Chrome Extensions, by default.” It outlines upcoming changes to Chrome’s extension architecture designed to make “extensions trustworthy by default.” I thought it would be interesting to explore each of the announced changes and compare them to what Mozilla has built into Firefox.

User Controls for Host Permissions

“Beginning in Chrome 70, users will have the choice to restrict extension host access to a custom list of sites, or to configure extensions to require a click to gain access to the current page.”

Being able to review and modify the sites that an extension has access to, especially those extensions that ask to “access your data for all websites,” is a worthy goal. Mozilla has discussed similar ideas, but the problem always comes down presenting this in a clear, uncomplicated way to a majority of users.

Having played a bit with this feature in Chrome, the implementation definitely seems targeted at power users. Extensions that request access to all websites still get installed with that access, so the default behavior has not changed.

The click-to-script option is intriguing, although the UX is a bit awkward. It’s workable if you have a single extension, but becomes unwieldy to click and reload every site visited for every installed extension.

Admittedly, getting this interface right in an intuitive and easy-to-use manner is not straightforward and I applaud Google for taking a shot at it. Meanwhile Mozilla will continue to look for ways Firefox can provide more permission control to a majority of extension users.

Extension Review Process

“Going forward, extensions that request powerful permissions will be subject to additional compliance review.”

The post is vague about exactly what this means, but it likely means these extensions will be flagged for manual review. This brings Chrome up to the standard that Firefox set last year, which is great news for the web. More manual review means fewer malicious extensions.

“We’re also looking very closely at extensions that use remotely hosted code, with ongoing monitoring.”

Firefox expressly forbids remotely hosted code. Our feeling is that no amount of review can eliminate the risks introduced when developers can easily and undetectably change what code is loaded by extensions. Mozilla’s policy ensures that no unreviewed code is ever loaded into the browser, and enforced signatures prevents reviewed code from being altered after release.

Code Readability Requirements

“Starting today, Chrome Web Store will no longer allow extensions with obfuscated code…minification will still be allowed.”

In reality, minified and obfuscated code are not very useful in extensions. In both Chrome and Firefox, extensions load locally (not over the network) so there is almost no performance advantage to minification, and obfuscation can be overcome by a dedicated person with readily available tools and sufficient effort.

Nevertheless, Mozilla permits both obfuscated and minified extensions in our store. Critically, though, Mozilla requires all developers to submit original, non-obfuscated, non-minified code for review, along with instructions on how to reproduce (including any obfuscation or minification) the store version. This ensures that reviewers are able to review and understand every extension, and that the store version is unaltered from the reviewed version.

As you might expect, this takes a significant investment of time and energy for both Mozilla and developers. We believe it is worth it, though, to allow developers to secure their code, if desired, while simultaneously providing thoroughly reviewed extensions that maintain user security and privacy.

Required 2-Step Verification

As a whole, the web is moving in this direction and requiring it for developer accounts is a strong step towards protecting users. Mozilla recently added two-step authentication for Firefox Sync accounts, and two-step authentication for Firefox extension developers is on the roadmap for the fourth quarter of 2018. Like Google, we expect to have this feature enabled by 2019.

Manifest v3

“In 2019 we will introduce the next extensions manifest version…We intend to make the transition to manifest v3 as smooth as possible and we’re thinking carefully about the rollout plan.”

In 2015, Mozilla announced we were deprecating our extremely popular extension system in favor of WebExtensions, an API compatible with Chrome, as well as Edge and Opera. There were several reasons for this, but a large part of the motivation was standards — a fundamental belief that adopting the API of the market leader, in effect creating a de facto standard, was in the best interests of all users.

It was a controversial decision, but it was right for the web and it represents who Mozilla is and our core mission. Three years later, while there still isn’t an official standard for browser extensions, the web is a place where developers can quickly and easily create cross-browser extensions that run nearly unchanged on every major platform.

So I would like to publicly invite Google to collaborate with Mozilla and other browser vendors on manifest v3. It is an incredible opportunity to show that Chrome embodies Google’s philosophy to “focus on the user,” would reaffirm the Chrome team’s commitment to open standards and an interoperable web, and be a powerful statement that working together on the future of browser extensions is in the best interests of a healthy internet.


While all of the changes Google outlined are interesting, some of them could go a step further in protecting users online. Nevertheless, I’d like say — bravo! The motivation behind these changes is definitely in the spirit of Mozilla’s mission and a gain for the open web. With Chrome’s market share, these initiatives will have a positive impact in protecting the security and privacy of millions of users around the world, and the web will be a better place for it.

A lot of work remains, though. Expect Mozilla to keep fighting for users on the web, launching new initiatives, like Firefox Monitor, to keep people safe, and advancing Firefox to be the best user agent you can have in your online journies.

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Updates to Add-on Review Policies


The Firefox add-ons platform provides developers with a great level of freedom to create amazing features that help make users’ lives easier. We’ve made some significant changes to add-ons over the past year, and would like to make developers aware of some updates to the policies that guide add-ons that are distributed publicly. We regularly review and update our policies in reaction to changes in the add-on ecosystem, and to ensure both developers and users have a safe and enjoyable experience.

With the transition to the WebExtensions API, we have updated our policies to better reflect the characteristics of the new technology, and to better clarify the  practices that have been established over the years.

As existing add-ons may require changes to comply with the new policies, we would like to encourage add-on developers to preview the policies, and make any necessary preparations to adjust their add-ons.

Some notable changes and clarifications include:

  • With some minor exceptions for add-ons listed on, all policies apply to any add-ons that are distributed to consumers in any manner.
  • Add-on listings should have an easy-to-read description about everything it does.
  • Add-ons that contain obfuscated, minified or otherwise machine-generated code, must provide the original, non-generated source code to Mozilla during submission as well as instructions on how to reproduce the build.
  • Add-ons that collect, store, use or share user data must clearly disclose the behavior in the privacy policy and summarize it in the description. Users must be provided with a way to control the data collection.
  • Collecting data not explicitly required for the add-on’s basic functionality is prohibited. Add-ons must only collect information about add-on performance and/or use.

If you have questions about the updated policies or would like to provide feedback, feel free to reply on the discourse thread.

The new policies will be effective April 1, 2018.

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Extension review wait times are about to get much shorter


One the of the main advantages of the new WebExtensions API is that it is less likely to cause security or stability problems for users. This means we can review these add-ons faster, and we have adapted our review flow accordingly. For the past few months we have reduced review wait times for add-ons written using the WebExtensions API. Today we’re taking another big step in that direction.

Add-ons built on the WebExtensions API will now be automatically reviewed. This means we will publish add-ons shortly after uploading. Human reviewers will look at these pre-approved add-ons, prioritized on various risk factors that are calculated from the add-on’s codebase and other metadata. This change is now live, and we plan to continue augmenting it in the coming months.

These changes give developers a much improved upload and publishing experience, but also comes with more responsibility on their end. Issues that arise during review can still lead to rejection of a version or a whole listing. This will now happen after publication, rather than before. We’re in the process of editing a new Review Policy that will make the rules, exceptions, and consequences clearer for everyone.

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