Many gecko/firefox devs work on Macs, so it is very surprising to hear that, unless your are running a somewhat old and unsupported version of MacOS (you need 10.7 according to https://developer.mozilla.org/en-US/docs/Mozilla/Developer_g...).

Oddly my impression is that their focus is more on Mac and Windows than on Linux. I swear that whenever i see them presenting something, it is invariably done using a Mac.