Downstream bug: https://bugzilla.mozilla.org/show_bug.cgi?id=916950
So last I tested this I couldn't get it to work on an unagi device running 1.1 prerelease, but it worked fine running on Android devices.
Still seems pretty flaky on v1.2 local build on my ZTE Open, I'll try and investigate what's going on; if I can't get it to work I'll pull the feature for now.
Version: unspecified
Severity: normal