Since quite some time Windows64 ARM64 builds are provided for download and we don't support these yet. We can add support across all build types because they are shipped for daily, candidate and release builds.

• https://archive.mozilla.org/pub/firefox/nightly/latest-mozilla-central/firefox-127.0a1.en-US.win64-aarch64.installer.exe
• https://archive.mozilla.org/pub/firefox/candidates/126.0-candidates/build2/win64-aarch64/
• https://archive.mozilla.org/pub/firefox/releases/126.0/win64-aarch64/

See issue #680 for a similar addition for Linux ARM64.