The Contextual Identity API indicates that it's supported [1] in Firefox for Android so will need see how usable it is. I was planning on testing my extension on Android soon.

Looking into it more, there is an open request to complete the work in Android Firefox [2] and also to make the MAC extension for Android too [3]

1. https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/Web...

2. https://bugzilla.mozilla.org/show_bug.cgi?id=1807456

3. https://connect.mozilla.org/t5/ideas/multi-account-container...