Yeah, the official Firefox build unfortunately depends on some proprietary libraries, which are removed by Fennec.
Fennec is just a collection of patches to remove that from the official Firefox repo: https://gitlab.com/relan/fennecbuild
Generally, I would recommend using Fennec, yes.
If you want the official Firefox builds without using the Play Store, FFUpdater is useful: https://f-droid.org/packages/de.marmaro.krt.ffupdater/