At Mozilla, we know that creating compelling web experiences depends on the ability to test sites across all browsers. This means that enabling excellent cross-browser automation is a key part of how we deliver our vision for the open web.

Today, we are excited to share a significant milestone: Cypress will use WebDriver BiDi as its default automation protocol for Firefox 135 and later, starting with Cypress 14.1.0.

Why WebDriver BiDi?

WebDriver BiDi is a cross-browser automation protocol undergoing standardisation at W3C. It is designed as an update to the existing WebDriver standard that provides the two-way communication and rich feature set required for modern testing tools.

Prior to WebDriver BiDi, browser testing tools such as Cypress often used the Chrome Devtools Protocol (CDP) to gain access to functionality not available in WebDriver. However this comes with a significant disadvantage: as the name suggests the Chrome Devtools Protocol is only available in Chromium-based browsers, significantly limiting its suitability for cross-browser testing. For more information on the relationship between CDP and WebDriver BiDi, see our posts on the hacks blog.

To help bridge this gap, back in 2019 Firefox started to implement a subset of CDP directly in Gecko. This has been used by Cypress as part of their Firefox backend since version 4.0. However with WebDriver BiDi now offering a richer feature set and undergoing continual improvements, we believe that switching to the standard protocol will better serve the needs of Cypress users.

If you use Cypress and run into difficulties, it is temporarily possible to switch back to the CDP backend by setting the environment variable FORCE_FIREFOX_CDP=1. If you need to do this please file a bug. Cypress are planning to deprecate support for this in version 15 and the CDP support in Firefox will be removed after the next ESR release.

You can also check out the Cypress team’s blog post about the change.

Close Collaboration for a Seamless Transition

This achievement would not have been possible without the close collaboration between Mozilla and Cypress. From initial planning to implementation and testing, we worked together to ensure WebDriver BiDi meets the needs of Cypress users. This underscores our commitment to providing developers with powerful and reliable tools for cross-browser testing.

CDP Support Ends with Firefox 141

As we continue transitioning to WebDriver BiDi, support for the experimental Chrome DevTools Protocol in Firefox will officially end with Firefox 141, set for release on July 22nd. The 140 ESR release will continue to have CDP support for its full support lifecycle. Removing the CDP implementation will allow us to focus our efforts entirely on improving WebDriver BiDi.

What’s Next?

We believe that WebDriver BiDi provides a solid foundation for the future of browser testing and automation. We will continue to work closely with automation tools to ensure that it meets their needs for a robust, feature-rich, cross-browser automation protocol.

Stay tuned for further updates as we continue improving the Firefox automation experience. The future of automation is here, and WebDriver BiDi is leading the way!