I remember when inbox launched it could be only used under chrome/chromium. Then somebody changed their user agent in firefox to chrome and magically it started working just fine. So you might want to try that.
Edit: Paul Kinlan reports that Earth is using PNaCl (https://twitter.com/Paul_Kinlan/status/854351477506277378), which means it fundamentally can't run outside of Blink.
Reminds me of the good old days of ActiveX!
Incorrect, PNaCl runs on both ARM and Intel.
NaCl (without the P) had to be separately compiled for different platforms, PNaCl is portable.