UA string no longer reveals 32-bit Firefox running on 64-bit OS

Published: | Categories: Networking


Previously, the user agent (UA) string of Firefox was revealing the fact that the user was running the 32-bit version of Firefox on a 64-bit operating system by saying “WOW64” or “Linux i686 on x86_64”. This was needed particularly to detect the browser compatibility with Adobe Flash Player, but the current plug-in installer comes with both the 32-bit and 64-bit versions, and Flash Player has been deprecated anyway.

Firefox 69 has removed the extra information from the UA string, so it now simply says “Win64” or “Linux x86_64” in the User-Agent HTTP request header as well as the navigator.userAgent, navigator.platform, and navigator.oscpu DOM APIs.

This change is expected to reduce UA fingerprinting factors, and improves the UX on software download sites which should be serving a 64-bit application to a 64-bit OS even if the user is running the 32-bit version of Firefox.