[Feature]: Resolve mismatch between Playwright and public juggler version

[leeN]

🚀 Feature Request

Since v1.61.0, custom Firefox builds are broken with Playwright. The suggestion would be to update the browser_patches/juggler.

Example

Custom Firefox forks could be used with Playwright again; this used to be painless, but is sadly impossible at the moment.

Motivation

Currently, the protocol differs between Playwright and Juggler (https://github.com/microsoft/playwright/blob/main/browser_patches/firefox/juggler/protocol/Protocol.js#L79 <-> https://github.com/microsoft/playwright/blob/main/packages/playwright-core/src/server/firefox/protocol.d.ts#L209), and the additional isMobile flag causes a crash when creating a new Context.

The error message is:

browser.newContext: Protocol error (Browser.setDefaultViewport): ERROR: failed to call method 'Browser.setDefaultViewport' with parameters {
"browserContextId": "81e60b08-fc7d-4f70-961d-fd9e808d95ac",
"viewport": {
"viewportSize": {
"width": 1280,
"height": 720
},
"deviceScaleFactor": 1,
"isMobile": false
}
}
Found property ".viewport.isMobile" - false, which is not described in this scheme
at async /home/user/Projects/playwright_tests/index.js:17:21 {
log: [],
name: 'Error'
}

The following commit causes this: #41179; i.e., the required juggler changes are not public. There was a PR (#41181), but it got closed due to some issue. These issues apparently have been resolved, as there has been a release (1.61) since then; the roll PR for Firefox is at #41249. This change has sadly not been reflected in the juggler folder.

Is this for a specific reason? I'm aware that this is not an actively supported configuration and do not need any help with the code itself. I would like to continue building Firefox forks that support Playwright.

[pavelfeldman]

What are you trying to do?

[leeN]

Hi,

I'm one of the maintainers of Project Foxhound, a Firefox fork for security testing. Since 2022, we've supported browser automation with Playwright — through prebuilt binaries, how-to guides, and project templates.

Playwright has become the main way our users automate Foxhound, both for large-scale web studies in academia and for industrial testing tools built on top of it. It's been a great fit, and we're really happy with the integration.

This all depends on being able to compile Foxhound with Juggler and the Playwright patches applied. We've automated that on our end with a build script, so the integration details stay hidden from the user.

To be clear, we don't expect any support from you. If incompatibilities arise from changes we make to Foxhound, that's on us to fix. To the best of my knowledge, every user issue about the integration so far has been reported to and resolved by us. So we don't anticipate this creating any maintenance burden for you beyond keeping the code available.

In short: we'd be very grateful if the Juggler/browser patches could remain available, as they're what allows us to keep supporting an integration our users and we value a great deal.

Thanks so much for your work on Playwright!