I do not fear telemetry. What I refuse to accept from Firefox is a FOSS product being as bad if not worse as Chrome on the telemetry and data collection front.

I like uBO but you can replace it with a dns filtering service for 95% of its use case (ad blocking).

It could just be me but I do not see browser extensions on mobile as a killer feature. Moreso, when the same extensions are primarily developed for desktop.