Some of those are for optional features like WebRTC, they are not all needed for a functional browser.
Re:Haiku OS ported and running on RISC-V
by codetrotter on Wednesday May 12, 2021 @06:15PM
(#27135810)
This thread is about fully featured browsers though. I think without WebRTC you can not call the browser fully featured.
Presumably the use of rust is a dependency that needs fulfilled for building FF. Looks like there has been some work on getting rust to play with Haiku at both the Rust and Haiku ends:
https://docs.rs/haiku/0.2.0/haiku/
https://www.haiku-os.org/blog/nielx/2020-09-06_rust_on_haiku...