It's possible to build it without those problems (see Fennec on F-Droid in fact), but it takes a lot of time for someone to create a recipe, and it's prone to break on every upgrade (and that's why the last version of Fennec on F-Droid is based on Firefox 40).
I don't know if/how many of those problems apply on Firefox OS (I guess at least the complex build environment applies), but that's likely why you'll not find it on F-Droid anytime soon. Unless someone decides to pour lots and lots of energy into this.
More info/sources:
https://f-droid.org/wiki/page/org.mozilla.firefox
https://f-droid.org/wiki/page/org.mozilla.fennec_fdroid
https://gitlab.com/fdroid/fdroiddata/blob/master/metadata/or...
>It's possible to build it without those problems (see Fennec on F-Droid in fact)
Fennec is stuck on 40 because of difficulties with building it, and even when one person managed to build it, .apk didn't start on others developers phone. A few people tried upgrading it to 41 and all failed, I guess fennec is kill now. I talked about it a few times on their IRC with people responsible for fennec.
It should not be a problem basing it on B2G.