Add-on sync only works between similar Firefox installations. For example, if you install an add-on on desktop Firefox, it will only sync to other desktops, not to your Android device running Firefox.

Note: Add-on sync currently only works on desktop Firefox and Firefox for tablets. It doesn't work on Firefox for smaller mobile devices.
https://support.mozilla.org/en-US/kb/sync-your-add-ons-another-copy-firefox

Nevertheless, it would be very helpful if some workaround could be devised.