WebDriver is a remote control interface that enables introspection and control of user agents. As such it can help developers to verify that their websites are working and performing well with all major browsers. The protocol is standardized by the W3C and consists of two separate specifications: WebDriver classic (HTTP) and the new WebDriver BiDi (Bi-Directional).

This newsletter gives an overview of the work we’ve done as part of the Firefox 126 release cycle.

Contributions

With Firefox being an open source project, we are grateful to get contributions from people outside of Mozilla:

• Gravyant improved the error message for the session.new command when no capabilities are specified.

WebDriver code is written in JavaScript, Python, and Rust so any web developer can contribute! Read how to setup the work environment and check the list of mentored issues for Marionette.

WebDriver BiDi

New: Support for the “contexts” argument for the “network.addIntercept” command

Since the introduction of the network.addIntercept command in Firefox 124, users could only apply network interceptions globally, affecting all open web pages across various tabs and windows. This necessitated the setup of specific filters to limit the impact to tabs requiring interception. However, this approach adversely affected performance, particularly when client code didn’t run locally, leading to increased data transmission over the network.

To address these issues and simplify the use of network interception for specific tabs, we’ve added the contexts argument in the network.addIntercept command. This enhancement facilitates the targeting of specific top-level browsing contexts, enabling the restriction of network request interception to individual tabs even with the same web page open in multiple tabs.

Bug fixes

• Both the commands session.subscribe and session.unsubscribe now raise an invalid argument error when the value of the arguments events or contexts are empty arrays.
• Updated the implementation of the storage.getCookies command to align with the Gecko default cookie behavior. This allows the removal of the user value for the preference network.cookie.cookieBehavior, which was only expected to be set for our experimental CDP implementation.
• Removed the ownership and sandbox arguments for the browsingContext.locateNodes command because they are no longer necessary.