As mentioned elsewhere in this thread, the Google SDK is only used to record whether the app was installed by way of an ad campaign Mozilla is running on Google. All other telemetry data goes directly to Mozilla servers, and contains things like "feature X was used"—not browsing data.
That is not actually what I said. The only component we use for campaign tracking is Adjust which has nothing to do with google services. Adjust has gone through a very tough vetting process.
> - Adjust SDK: an install attribution tool (aka install referrer tracking). This is only used to determine whether the app was installed as the result of a specific (google-hosted) ad campaign. Adjust depends on play-services-analytics. ( https://www.adjust.com/glossary/install-referrer/ ).
play-services-analytics is what I meant by "the Google SDK" in question; sorry if that was unclear!
Since it's all free software, you can check what events are actually sent here: https://github.com/mozilla-mobile/focus-android/blob/master/...