If you are trying to switch from Chrome, then just use regular Firefox with the ublock extension (and maybe some of the other privacy extension officially supported). If you are a “power user” and want modify/access about:config and other settings then you need Firefox Nightly. The Fennec and Fenix (iirc) are just stripped down Firefox that either only have private mode or additional settings for privacy (that are already present in regular version, but way not be enabled by default). Hope that helps.