Firefox for Android’s Play Integrity check hits custom ROMs

Mozilla has added Google’s Play Integrity API to Firefox for Android, requiring a token from the API to access the browser’s server-side AI tools. The change, documented in Mozilla’s public tracker, blocks users of custom ROMs and non-Google-certified devices from using features like Smart Window, as the token verifies the browser is an unmodified copy installed via the Play Store. This move restricts access to Mozilla’s compute infrastructure to only Play-installed Firefox versions on certified devices.

Mozilla has added support for Google’s Play Integrity API, known for blocking users of custom ROMs from accessing banking apps, to Firefox for Android. Per a resolved issue in Mozilla’s public tracker, a new lib-integrity-googleplay library was added to Firefox’s Android codebase. It requests a Play Integrity token which is then passed to Mozilla’s MLPA Machine Learning Proxy server. The token is used to access Firefox’s server-side AI tools, like Smart Window, for rate-limiting purposes, ensuring only unmodified, Play-installed copies of Firefox on Google-certified devices use Mozilla’s compute infra. Per documentation for the API, developers can: “…call the Integrity API … to … You're reading Firefox for Android’s Play Integrity check hits custom ROMs https://www.omgubuntu.co.uk/2026/06/mozilla-firefox-android-google-play-integrity , a blog post from OMG Ubuntu https://www.omgubuntu.co.uk . Do not reproduce elsewhere without permission.