The NodeJS dependency is purely for running some tests. You shouldn't need it to actually build Firefox.
If that was the case I'm sure someone would've turned it into a test-only dependency in gentoo.
So actually even Firefox depends on V8...
What’s wrong with V8? Had only pleasant interactions with it so far (maybe compiling takes long, can’t tell, whole webkit is a nightmare in that regard)
Oh it's perfectly fine, but Firefox was kind of the only illusion that the web does not rely on a single implementation, so discovering that even that depends on V8 is kind of funny :)