Hide navigator.webdriver via [Pref] gate in WebIDL

[barbatus]

Summary

patches/playwright/1-leak-fixes.patch already drops Navigator::Webdriver() to return false at the C++ level — but the webdriver attribute on Navigator is still exposed by WebIDL. Anti-bot platforms like FingerprintJS, DataDome and PerimeterX check the presence of navigator.webdriver

Description

Two new hunks added to 1-leak-fixes.patch:

1. modules/libpref/init/StaticPrefList.yaml — declare a new static pref dom.webdriver.enabled (default false). Required because WebIDL [Pref="x.y.z"] resolves at build time to mozilla::StaticPrefs::x_y_z;

2. dom/webidl/Navigator.webidl — add Pref="dom.webdriver.enabled" to the existing [Constant, Cached] extended-attribute bracket on the webdriver attribute. When the pref is false, the WebIDL binding code generator omits the attribute from the prototype entirely; 'webdriver' in navigator returns false, matching vanilla Firefox.

                                                                                                                                                                                                                                                       ## Type of Change                                               
   

• Bug fix
• New feature
• Documentation update
• Other

Testing

Quick local repro:

import asyncio                                                                                                                                                                                                                                                              
from camoufox.async_api import AsyncCamoufox                                                                                                                                                                                                                                
                                                                                                                                                                                                                                                                            
async def main():
    async with AsyncCamoufox(headless=True) as browser:                                                                                                                                                                                                                     
        page = await browser.new_page()                         
        await page.goto("about:blank")  
        present = await page.evaluate("'webdriver' in navigator")
        value   = await page.evaluate("navigator.webdriver")                                                                                                                                                                                                                
        print(f"  'webdriver' in navigator = {present}")
        print(f"  navigator.webdriver       = {value}")                                                                                                                                                                                                                     
                                                                
asyncio.run(main())                                                                                                                                                                                                                                                         

Fingerprint Report

This PR specifically targets a fingerprint surface (navigator.webdriver exposure). Build-tester run pending — happy to attach if a maintainer requests it. Expected delta on the score: positive (one fewer detectable signal).

Fingerprint report

(to be attached after build-tester run; happy to coordinate)

Checklist

• I have linked a related issue above — none open; happy to file one if preferred
• My changes are focused on a single logical change
• I have added testing instructions which include the desired result
• Service tests pass — temporarily out of service per template
• Build test passes — pending; this PR adds a new static pref so the build must recompile WebIDLPrefs.cpp; would appreciate a maintainer's confirmation that the score improves