Abrowser can't log in to Firefox Sync (problem in about:accounts)

When attempting to sign in to an existing Firefox Sync account (I haven't tried with creating a new account) in Abrowser (via about:accounts), it loads for a while, then says "working" and might eventually have an "unexpected error". This problem does not exist in IceCat.

This has been mentioned a couple of times on the forum (such as https://trisquel.info/es/forum/abrowser-sync-doesnt-work).

I believe that the issue is that browser/base/content/aboutaccounts/aboutaccounts.js has erroneously had the event name "FirefoxAccountsCommand" changed to "AbrowserAccountsCommand"; it should have been left alone (it was left alone in IceCat).