1763310 - Report ARM64 Windows 11+ as "x86_64" (and continue to report Windows 10 as "x86")

Status: RESOLVED FIXED

(Core :: Networking: HTTP, enhancement, P2)

Description

[Chris Peterson [:cpeterson]]

ARM64 Windows 11+ supports x86_64 emulation, but Windows 10 only supports x86 emulation.

Advantages of reporting ARM64 Windows 11+ as x86_64:

• Sites that offer software downloads will know that the client is capable of running x86_64 software.
• Reduced fingerprinting entropy because ARM64 Windows 11+ users' UA string will match the UA string of the ~80% of Windows Firefox users running x86_64 instead of the ~20% running x86.
• Some sites disable features for 32-bit clients, such as Google Meet requiring 64-bit to use wasm visual effects:
  • https://github.com/WICG/ua-client-hints/issues/217#issuecomment-878537336
  • https://support.google.com/meet/answer/10058482?expand_all_zippies=true#requirements&zippy=%2Cwhy-cant-i-use-the-change-background-option%2Crequirements-to-apply-visual-effects-on-computer

CAVEATS:

• I do not have an ARM64 Windows machine to test on! But I confirmed that the correct x86_64 UA string is produced by adding some temporary assertions on an Windows aarch64 try run.
• The browser_navigator.js test is not actually run on ARM64 Windows in automation! But I these test changes should make the test pass on ARM64 Windows 10 and 11 if this test ever is run.
• Because I don't have an ARM64 Windows machine, I have not tested Google Meet's wasm visual effects to verify they are performant or even work. But if they don't, then users can choose to not enable them. That choice isn't even available today for Firefox users on ARM64 Windows users (because its UA looks like 32-bit Windows' x86 UA).

Comment 1

[Chris Peterson [:cpeterson]]

Attachment: Bug 1763310 - Report ARM64 Windows 11+ as "x86_64" (and continue to report Windows 10 as "x86"). r?#necko-reviewers!,hsivonen

Windows 11+ supports x86_64 emulation, but Windows 10 only supports x86 emulation.

Advantages of reporting ARM64 Windows 11+ as x86_64:

• Sites that offer software downloads will know that the client is capable of running x86_64 software.

• Reduced fingerprinting entropy because ARM64 Windows 11+ users' UA string will match the UA string of the ~80% of Windows Firefox users running x86_64 instead of the ~20% running x86.

• Some sites disable features for 32-bit clients, such as Google Meet requiring 64-bit to use wasm visual effects:

https://github.com/WICG/ua-client-hints/issues/217#issuecomment-878537336

https://support.google.com/meet/answer/10058482?expand_all_zippies=true#requirements&zippy=%2Cwhy-cant-i-use-the-change-background-option%2Crequirements-to-apply-visual-effects-on-computer

The browser_navigator.js test is not actually run on ARM64 Windows in automation, but these test changes would make the test pass on ARM64 Windows 10 and 11 if this test ever is run.

Comment 2

[Henri Sivonen (:hsivonen)]

Try build for experimentation:
https://treeherder.mozilla.org/#/jobs?repo=try&revision=30b8e6024371e8d40071e316b203d46a3b7e74da

Comment 3

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/a5ed35f83fea
Report ARM64 Windows 11+ as "x86_64" (and continue to report Windows 10 as "x86"). r=hsivonen,necko-reviewers,dragana

Comment 4

[Cristina Cozmuta (:CrissCozmuta)]

https://hg.mozilla.org/mozilla-central/rev/a5ed35f83fea