Mozilla seems to have quietly integrated a Google Play Integrity API check into the Firefox for Android codebase a few months ago. The code went live with Firefox 149 and requires the browser to request a verification token from Google. The app then passes this token to Mozilla’s machine learning proxy server.

It looks like this whole system exists just to gatekeep Firefox’s new server-side AI features. Tools like Smart Window rely on heavy processing power that lives on third-party servers. Mozilla proxies these requests to manage their rate limits. They evidently chose Google’s attestation system to verify that the traffic originates from an unmodified app binary on a certified device.

Users running custom ROMs usually fail these strict integrity checks. You probably recognize this exact verification system from banking apps or restrictive mobile games. It appears Firefox users with unlocked bootloaders will find themselves locked out of the new AI perks.

The browser itself still installs and loads web pages normally. You aren’t totally blocked from using Firefox on a modified device.

But it still stings. Firefox built a massive mobile user base by acting as a privacy-focused alternative to Chrome. Dedicated privacy advocates regularly install de-Googled operating systems like GrapheneOS or LineageOS to escape big tech tracking. These ROMs actively get rid of Play Services, so the very same users are treated as untrusted by the browser they used for years.

App developers have other device attestation methods available that don’t rely entirely on Play Services. There were even requests to explore less restrictive options in the past. The integration of the lib-integrity-googleplay library suggests they ultimately took the easiest route available. They forced a Google-operated verification layer into an app people use specifically to avoid Google.

This move by Mozilla would’ve probably stayed hidden if it weren’t for security experts discussing it on Mastodon and then highlighted by OMG Ubuntu.

Several security researchers in the thread voiced their frustration over the move. They argue the Play Integrity API doesn’t even properly solve the server abuse problem Mozilla is trying to fix. Some dedicated users already opened new bug reports begging the developers to reconsider and strip the proprietary check out entirely.

We’re yet to see real-world reports from users on custom ROMs complaining about this, but with the company pushing hard into AI integrations to find new profit streams, they obviously need to protect the servers running those expensive features. Choosing Google Play Integrity to handle that job alienates the exact power users who keep Firefox relevant on Android.

On the flip side, though, a lot of folks flipping to GrapheneOS or other privacy-focused ROMs most likely also want to escape the AI push. So for them, this is a win.

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