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 wh

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.