As far as I am aware these "features" are not removed per-say. Its just that
by default EME and telemetry are turned off which can be done in mainline
Firefox as well. Firefox ships with EME opt-in only, but I believe Telemetry
is on by default. Beyond that there is the branding and the add-on repo as
well. Pocket is removed too.
Icecat/Abrowser are ESR as apposed to stable. Normally this isn't a problem,
but with Quantum serving as a significant upgrade I can understand why people
would want to dump an ESR rebrand for mainline Firefox. Especially if they
fall in the "branding is not software" camp, which is a legitimate point.
Icecat/Abrowser do not have support for Sync, so there might be a freedom
issue there I am not aware of.
