Update from Mozilla:
You’re better off changing the PKGBUILD file to set
MACH_BUILD_PYTHON_NATIVE_PACKAGE_SOURCEto eitherpipornone.systemis really meant for use in Mozilla CI builds where compatibility is ensured. Per FS#75848, the Firefox package is usingpipto deal with this same issue.
See Using third-party Python packages — Firefox Source Docs documentation for what the different values forMACH_BUILD_PYTHON_NATIVE_PACKAGE_SOURCEare. I just built the Arch package with this diff applied and settingMACH_BUILD_PYTHON_NATIVE_PACKAGE_SOURCEtonone. That’s probably the way to go so you’re not relying on PyPi services to build.
FWIW, you should be able to removeyasm,imake,xorg-server-xvfb, andautoconf2.13frommakedependsand addjson-cas a dependency along withac_add_options --with-system-jsoncin mozconfig.cfg. The--disable-elf-hackline should be safe to remove from mozconfig.cfg as well.
I’m going to mark this WONTFIX, as updating PKGBUILD is the preferred fix.