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CDP removed in Firefox Nightly 141

In May 2024 we announced that our experimental support for the Chrome DevTools Protocol (CDP) was being deprecated in Firefox 129, and we were looking at removing it completely by the end of 2024. It has taken a bit more time to make sure libraries and clients could migrate to WebDriver BiDi, but here we are one year later to follow up on that plan.

We just landed the patch which completely removed our CDP implementation from Firefox. This removal is currently only in the Nightly channel, but if everything goes as expected Firefox 141 will be the first Firefox version where you can no longer use CDP. This means you can no longer opt-in using CDP with the remote.active-protocols preference, which has also been removed.

Our previous post about deprecating CDP in Firefox already detailed why we decided to make this move, so you can refer to it for more context. Here, I will focus on what actually changes for users and clients.

Test automation libraries

Since we started working on WebDriver BiDi, we collaborated closely with the major automation libraries in the ecosystem and we wanted to be sure that they had all the time and support to fully migrate out of our CDP implementation. Since the deprecation announcement last year, Puppeteer officially switched to WebDriver BiDi for Firefox, and earlier this year fully removed the CDP support for Firefox. Cypress also starting using WebDriver BiDi by default for Firefox. Selenium APIs relying on CDP were also migrated to WebDriver BiDi. And while Playwright’s support for WebDriver BiDi is still a work in progress, they were not using our CDP implementation either, so they are not impacted by this change.

If you are writing tests or tools with any of the libraries and frameworks listed above, nothing actually changes for you because they all migrated from CDP for Firefox already. To our knowledge, all major automation tools and libraries should work fine with Firefox 141.

Tools or scripts still using CDP

We are aware that outside the major automation libraries people may have specific tools or scripts that depend on CDP. If you are in this situation, we recommend that as a transitional measure you switch to using Firefox 140 ESR.

As an ESR release this will continue to get important security and stability updates, typically for one year. To use CDP in this release you will need to set the remote.active-protocols preference.

Migration from CDP to WebDriver BiDi

We strongly encourage anyone maintaining tools that still depend on CDP support in Firefox to migrate to WebDriver BiDi. Although there are differences, the protocol is similar enough to CDP that we believe most migrations should be straightforward. If you need help, please reach out to us on our discussion channel, or file a bug if you think you have found a defect in our implementation.

And if you are migrating a tool from CDP to WebDriver BiDi for Firefox, you should also consider using WebDriver BiDi for Chromium based browsers. Chromium has a great support for WebDriver BiDi, and WebKit is starting to implement BiDi as well. So switching to BiDi now is not only a way to keep Firefox support, but it can also pave the way to get more features for all browsers as we keep expanding the standard protocol.

Thanks for supporting Firefox automation

Removing our experimental CDP implementation will allow us to focus completely on implementing WebDriver BiDi to build a healthier testing ecosystem for the Web. Having a standardized protocol for browser automation is the way forward to make sure people can build tools and libraries against a stable set of commands and APIs. We are really excited about the potential for browser tooling based on WebDriver BiDi and we encourage anyone to start tinkering with this. We would love to know about your experiments and ideas.

But we also want to thank all the maintainers who jumped onto supporting Firefox with CDP when we started implementing Chrome’s protocol a few years ago. WebDriver BiDi came as the natural evolution from this effort, and we hope you will join us on this next journey.