My opinion is that what Mozilla produces in the domain of programming languages is superior to what Google produces in the same domain. I make no claims comparing the two outside this domain.
Google has far more resources than Mozilla, and produces loads of great stuff in many domains.
I use both browsers daily (Aurora specifically, for Firefox) and have no preference between them. I have no opinion on their source code.
Google has been pretty influential in PL, especially in the PL/systems domain (MapReduce); just because they aren't designing so many mainstream languages doesn't mean people like Jeff Dean aren't putting their PL skillz to work. In fact, many of the heavy hitters at Google have PL backgrounds and do a lot of PL work, they are just pragmatic and realize that not all PL work involves overtly new languages.
And then there is what Holzle, Bak, Bracha, etc...are doing with Dart; and of course Pike with Go.
Google has far more resources than Mozilla, and produces loads of great stuff in many domains.
I use both browsers daily (Aurora specifically, for Firefox) and have no preference between them. I have no opinion on their source code.