A browser shouldn't have access to your accounts. That opens up a big attack surface.
https://hg.mozilla.org/mozilla-central/rev/1d77c3062662
Note that it's only enabled in Nightlies with no plans to ship.
https://support.mozilla.org/en-US/kb/how-firefox-android-use...
Doesn't list that permission. I see no reason why Pocket or Sync would require that permission, although Hello likely does.