What's the source for Apple, Mozilla (ok Facebook I'm less surprised) deploying Go?
Apple have posts for go jobs: http://www.golangprojects.com/golang-go-job-in-Senior-CDN-De...
There is also some conjecture that someone at Apple is writing a web scraper in Go: https://news.ycombinator.com/item?id=8567205
Mozilla have a product called Heka written in Go: https://blog.mozilla.org/services/2013/04/30/introducing-hek...
Facebook have a load of open source libraries written in Go: https://github.com/facebookgo
Most prominent Mozilla Go usage is Heka ( https://github.com/mozilla-services/heka ).
I don't know about Apple, but knowing a number of folks in infra and ops there, and their tendencies, I do not doubt it is in use in places.
Second, with support from most major shops, and being deployed even in companies such as Apple, Mozilla, Facebook and more, Go is hardly "fringe" at this moment.