As of Firefox for Android 44, a custom addon is no longer required to customize Firefox Accounts and Firefox Sync server URLs.
The documentation at https://docs.services.mozilla.com/howtos/run-sync-1.5.html and https://docs.services.mozilla.com/howtos/run-fxa.html has been updated and is now the canonical documentation for configuring custom servers in Firefox for Android.
The contents of this repository have been maintained in deprecated
for interested parties to inspect.