For Android users seeking a privacy-focused browser, Privacy Guides recommends Mull:
Mull is a privacy oriented and deblobbed Android browser based on Firefox. Compared to Firefox, it offers much greater fingerprinting protection out of the box, and disables JavaScript Just-in-Time (JIT) compilation for enhanced security. It also removes all proprietary elements from Firefox, such as replacing Google Play Services references.
Mull enables many features upstreamed by the Tor uplift project using preferences from Arkenfox. Proprietary blobs are removed from Mozilla’s code using the scripts developed for Fennec F-Droid.
Fennec F-Droid suffices to remove the telemetry.
Fdroid literally says fennec tracks you under “anti-features”, did I miss something?
They remove telemetry, such as the kind of telemetry causing the problems reported in this thread. They do not remove OCSP, safe browsing, Sync, and other things that connect to outside servers and therefore leak information about user activity. They do enable about:config so that those which are unwanted can be disabled.