I wonder how long and difficult it must be to get all the required dependencies to compile a modern web browser...
[two hours of obscure error messages later]
"You have v2.3030392.302 of dependency 113, you need to compile v2.3030392.300 in 32-bit first, then build the 64-bit version of v2.3030392.301 then ..."
You get all the compiler errors fixed and then it's on to round two... linker errors.
I could definitely see someone doing that with Firefox. They may already exist. I've just, from experience, had so much trouble with compiling large codebases.
On the bright side, the larger a codebase, often, the more popular. And the more popular, the more likely people will have EXACT dependencies listed.
https://developer.mozilla.org/en-US/docs/Mozilla/Developer_g... lists the actual set of libraries and whatnot needed; converting those to the relevant package names for the Linux distro of your choice is tedious, but not too hard.
For an old version, things could be more complicated, depending...