WebDriver conformance changes for Firefox 149

[lutien]

This PR contains all the changes to WebDriver BiDi and Marionette for the Firefox 149 release.

[github-actions]

Preview URLs (1 page)

• /en-US/docs/Mozilla/Firefox/Releases/149

External URLs (11)

URL: /en-US/docs/Mozilla/Firefox/Releases/149
Title: Firefox 149 release notes for developers (Beta)

• https://bugzil.la/1905086 (1 time) (Note! This may be a new URL 👀)
• https://bugzil.la/1936770 (1 time) (Note! This may be a new URL 👀)
• https://bugzil.la/1962355 (1 time) (Note! This may be a new URL 👀)
• https://bugzil.la/1985997 (1 time) (Note! This may be a new URL 👀)
• https://bugzil.la/1989022 (1 time) (Note! This may be a new URL 👀)
• https://bugzil.la/1994148 (1 time) (Note! This may be a new URL 👀)
• https://bugzil.la/2005546 (1 time) (Note! This may be a new URL 👀)
• https://bugzil.la/2005558 (1 time) (Note! This may be a new URL 👀)
• https://bugzil.la/2007385 (1 time) (Note! This may be a new URL 👀)
• https://bugzil.la/2008345 (1 time) (Note! This may be a new URL 👀)
• https://bugzil.la/2016673 (1 time) (Note! This may be a new URL 👀)

(comment last updated: 2026-03-20 13:59:11)

[whimboo]

I've some suggestions but otherwise it looks good to me. Thanks!

[whimboo]

To stay in sync with former release notes:

Suggested change

	- Implemented the `browser.setDownloadBehavior` command, which lets clients allow or prohibit the downloads and also set a custom download folder. This behavior can be configured per session or per user contexts. ([Firefox bug 1989022](https://bugzil.la/1989022)).
	- Added the `browser.setDownloadBehavior` command, which lets clients allow or prohibit the downloads and also set a custom download folder. This behavior can be configured per session or per user contexts. ([Firefox bug 1989022](https://bugzil.la/1989022)).

[lutien]

We use implemented in the notes for other releases (e.g., 145 or 147). I don't really see the clear pattern here (and I don't think we need it).

[pepelsbey]

I would say it’s easier to quickly parse release notes when every item starts with Added, Updated, Fixed. Ideally, they would be grouped in the same list or even into sections. With sections, we won’t even need Added, Updated, Fixed:

Added

• Support for automatic user prompt handling
• browser.setDownloadBehavior command

Updated

• Logic of applying different settings

Fixed

• Issue where the browsingContext.userPromptOpened
• Serialization for DOM nodes

[lutien]

Alright, that makes sense! To not introduce sections now (we can maybe discuss it for future updates), I, for now, just updated all the implement items to start with add and grouped them together.

[pepelsbey]

Looks good! Thank you 🙂

Left a non-critical opinion 😬

[pepelsbey]

I would say it’s easier to quickly parse release notes when every item starts with Added, Updated, Fixed. Ideally, they would be grouped in the same list or even into sections. With sections, we won’t even need Added, Updated, Fixed:

Added

• Support for automatic user prompt handling
• browser.setDownloadBehavior command

Updated

• Logic of applying different settings

Fixed

• Issue where the browsingContext.userPromptOpened
• Serialization for DOM nodes