Firefox Developer Experience

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Deprecating CDP Support in Firefox: Embracing the Future with WebDriver BiDi

Posted by

Henrik Skupin

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Starting with Firefox 129 support for the Chrome DevTools Protocol (CDP) in Firefox will be deprecated. Users of CDP in Firefox are encouraged to migrate to the W3C WebDriver BiDi protocol. This now offers a superset of the features that were provided by Firefox’s CDP implementation.

During the depreciation period users have two choices to continue to use CDP with Firefox:

  • Use the ESR 128 release, which will continue to have the same behavior as today throughout its entire support period of about a year.
  • Set the remote.active-protocols preference to 2 before starting Firefox.
  • If WebDriver BiDi should be enabled as well, set the remote.active-protocols preference to 3.

Our current expectation is to remove the CDP support entirely at the end of 2024.

Notably, Puppeteer users are not affected by the deprecation of CDP, as Puppeteer automatically sets the necessary preference based on the selected protocol (CDP or BiDi)

If you have a client or tool that currently uses CDP and you wish to continue supporting Firefox, we would appreciate a brief notification, even if you do not need any assistance. Having a list of such clients will help us reach out with important information ahead of any future protocol changes.

Also in case of any questions about transitioning to WebDriver BiDi, or concerns about this change, please reach out to us.

Fore more details about the background to this change, read on.

The History of CDP Support in Firefox

The implementation of the Chrome DevTools Protocol (CDP) in Firefox began as an initiative to provide access to modern web testing tools like Puppeteer, Cypress, and Browsertime, which are widely used and largely rely on the CDP protocol. The development kicked off in 2019 with the introduction of the Remote Agent component in Firefox, and by early 2020 experimental support for CDP was made available in Firefox Nightly builds. A significant milestone was reached in February 2021 with the release of Firefox 86, where CDP support was enabled by default, supporting 82 APIs – a subset of the full range of APIs available through CDP.

Enhancing Cross-browser Testing with Firefox

In a two-part series on Mozilla Hacks, we already explored the challenges and advancements in cross-browser testing.

The first post, Cross-browser Testing, Part 1: Web App Testing Today, discusses the complexities of ensuring web applications function seamlessly across different browsers. It highlights the need for improved testing tools to address inconsistencies caused by varied web standard implementations.

The second post, Improving Cross-browser Testing, Part 2: New Automation Features in Firefox Nightly, introduces new automation features in Firefox Nightly. These enhancements include improved WebDriver support and the new WebDriver BiDi protocol, aimed at providing more robust and reliable automation tools for developers. Our efforts in these areas are designed to simplify cross-browser testing and improve interoperability between browsers.

Adopting WebDriver BiDi in Puppeteer

With the rise of WebDriver BiDi, the Puppeteer team began integrating support for this new protocol. Today, WebDriver BiDi in Firefox offers a broader range of features than its experimental CDP implementation, making it a more powerful and flexible option for web automation and testing. This includes features like using pre-load scripts to monitor DOM updates, network interception, and better logging, which are critical for modern web applications.

We’ve been working with the Puppeteer team to enable BiDi-based support for Firefox, offering more features and higher quality than the previous CDP-based implementation. This shift reflects the growing industry preference for a standardized, cross-browser automation protocol. We believe this change will significantly improve automation workflows and ensure compatibility across different browser environments. Stay tuned as we finalize the implementation of the remaining required APIs. Our goal is to provide a seamless and enhanced automation experience for all users.

Deprecation of CDP

As Firefox moves towards fully embracing WebDriver BiDi, CDP support in Firefox was put into limited maintenance mode. This means that no new features, aside from the existing automation-related APIs, have been or will be added any more. Also with tools like Selenium, Browsertime, and Puppeteer adopting WebDriver BiDi as their communication protocol, we see no reason to continue supporting CDP in Firefox. Therefore, starting with Firefox 129, the CDP protocol will no longer be enabled by default. However, Firefox 128 ESR will continue to have CDP enabled for another year, providing a transition period for users.

Please note that the deprecation of CDP will not impact Puppeteer users, as we will wait until Puppeteer uses WebDriver BiDi by default for Firefox.

However, if you are using a different CDP client, you can manually enable the protocol by setting the Firefox preference remote.active-protocols to 2 before starting Firefox or by restarting the browser. If WebDriver BiDi should be enabled as well, set the remote.active-protocols preference to 3. Nonetheless, we strongly recommend migrating to WebDriver BiDi, as support for CDP is scheduled to be fully removed by the end of 2024.

Support and Collaboration

If you have any questions about WebDriver BiDi, please feel free to reach out to us. You can contact us via the Google dev-webdriver mailing list or join the conversation on Matrix in the #webdriver channel. We are here to answer your questions and provide guidance on using WebDriver BiDi to communicate with Firefox effectively.

Henrik Skupin

4 responses

  1. peterwx Avatar
    peterwx

    Not sure if it’s preferable to comment through here, or the other provided contact links at the end of your post.
    Google groups seems to have little anonymity of name and email and Matrix’s UI is not very suitable to write from a mobile device and the Webdriver channel seems to be full of technical content and contributors that I’m not sure would appreciate my mostly surface level comment/doubt on Webdriver usage ( never used any remote protocol, this would be a first ).
    If you prefer, I’ll engage again at Matrix’s.
    So, I think we already have had a past conversation about this, in which you said that browser automation like for example being able to take browser UI screenshots ( and possibly addon’s views/pages ) is possible only on Webdriver classic or CDP ( not BiDi ), if I remember correctly ?
    What impact non BiDi protocols removal at 2024’s end will have for someone who wants to keep using the latest non ESR release of Firefox ? Does one simply use Marionette, Geckodriver or Puppeteer ( which ) ?
    Also seems that Webdriver (BiDi ?) spec has provisions that allows for browsers companies to implement their own extensions to the spec. Can you confirm if that’s the case ?

    Thanks again for any new info provided and the older info ( I haven’t got yet to experiment with the links you provided for Webdriver protocol experimentation/testing ) .

    Reply
    1. Henrik Skupin Avatar
      Henrik Skupin

      Thanks Peter for the feedback. Also as you have reached out via Matrix we got all the questions solved over there. But I would like give a quick feedback here as well in case others have similar questions.

      * Screenshots of web pages can be done by any supported protocol, but those for the Firefox UI will only work with WebDriver classic (Marionette and geckodriver) at the moment.
      * The removal of CDP has no impact on Marionette, geckodriver and WebDriver BiDi. All these protocols will be maintained and further development happens to extend their feature sets.
      * As written in the post users of Puppeteer should not see an issue given that Puppeteer works already well with WebDriver BiDi, and before we switch the value of the preference we are waiting for a Puppeteer release with Webdriver BiDi enabled by default for its underlying protocol.
      * Other Web specifications already define extensions (like permissions, webauthn) to the WebDriver specs. So yes, the spec is extensible.

      Reply
  2. Steve Low Avatar
    Steve Low

    I have a few helper scripts that use –remote-debugging-port to use the CDP interface. When I upgraded firefox (to 129.0.2) these all broke because that CLI option changed to use BiDi. It took me half a day to figure this out (maybe I’m bad at reading or finding the firefox changelogs because I never found it in anything like that). It seems like the protocols are similar except BiDi doesn’t seem to support the “/json/list” http endpoint which is used in CDP. The docs are scarce on bidi (besides reading the full spec) and I gave up finding a quick way to replicate this in bidi.
    It would be nice if there were warnings/explanations about the –remote-debugging-port CLI arg having a major change it its meaning like this, and if there were a migration guide somewhere for those using it before turning off the support for CDP. It’s still unclear to me if that CLI arg is an offically supported way to do that?

    The firefox CDP docs are currently totally wrong: https://firefox-source-docs.mozilla.org/remote/cdp/Usage.html

    Reply
    1. Henrik Skupin Avatar
      Henrik Skupin

      Thank you for your feedback, Steve! We’re sorry to hear that the changes to CDP support in Firefox are causing you trouble. Please understand that CDP has always been an experimental implementation, and we communicated its deprecation through a blog post and our WebDriver mailing list.

      With the release of Firefox 129, we haven’t completely removed CDP support, but it is no longer enabled by default. If you’d like to continue using it, you can update the user preference `remote.active-protocols` as described above. The `–remote-debugging-protocol` option remains unaffected, as it controls the Remote Agent component, which handles both WebDriver BiDi and CDP.

      That said, we plan to fully remove CDP support by the end of the year, as WebDriver BiDi has become mature enough to handle most standard automation scenarios. While it doesn’t yet cover all CDP APIs, we are continually improving the protocol.

      If you’re interested in following these developments or considering a move to WebDriver BiDi, you can stay updated through our mailing list or join us in the referenced Matrix channel to get in touch. We’re also working on making more clients beside Puppeteer available for various languages to make it easier to interact with Firefox using WebDriver BiDi.

      Thank you for the hint about the outdated documentation as well. I’ve filed this bug to get it fixed.

      Best,
      Henrik

      Reply

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