I've created dev environment VM's with classic operating systems (XP, etc) because my job involves updating lots of really old code (most clients only update when they have to, every 5-10 years).

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.