What is the best version of Firefox that I can use it in android based on security and privacy.
The latest.
Point.
For security and privacy use mull it is a fork of Firefox and has very good tracking protection out of the box
I going to say mull because it’s a hardened version.
Fennec (available on fdroid) removes the already minimal tracking features in Firefox and is just as secure.
IMO firefox nightly, because it lets me run desktop extensions
IIRC Fennec (on F-Droid) also does this while sticking close to Stable otherwise (updates lag a few days behind usually).
Mull is the best Firefox fork on Android. Vanilla Firefox has trackers and telemetry by default and very little protection against fingerprinting.
See: DivestOS browser table for more info
I use Firefox Beta because it has extension supports, and I haven’t found critical bugs.
Beta… That defeats the point of security portion of the question.