I was looking for Firefox OS / Firefox for Mobile App Automation.
Although there is a Marionette , we can try: https://developer.mozilla.org/en-US/docs/Mozilla/QA/Marionette
I can't seem to find the Selenium library for testing Firefox OS applications. Is there any other way to test web applications in Firefox for Android / Firefox OS?
The basis of testing Firefox OS applications is what is generally used for automated testing on the platform. I'll point this out to get started, Marionette is a selenium, but a customized version optimized for use in instances of Mozilla Gecko.
https://developer.mozilla.org/en-US/docs/Archive/Firefox_OS/Automated_testing/gaia-ui-tests/Part_2_Marionette_Firefox_OS_interactions
This page will show you how to run interactions inside firefox os, and the part3 manual will show you how to create automated test scripts. Currently, Marionette will only work for Firefox os <= 2.5 at present, since the puppet does not work s> 2.5.