Anyway, https://ftp.mozilla.org/pub/firefox/releases/ has links to all the Firefox release binaries and corresponding source snapshots starting with version 0.8. It includes a number of the betas as well (so for example has the Firefox 58 beta builds already).
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...
So mostly you're talking about IE/Edge...