Talking with :snorp we think we might be get away with just exposing get and set to embedders.

Found this comment by Lina which looks relevant https://bugzilla.mozilla.org/show_bug.cgi?id=1626506#c4

This one seems to be supported already according to "GeckoView WebExtension API needs" document

I think the doc is not accurate, we don't support storage.sync, at least not across devices (it's basically a local-only implementation right now).

This lack of functionality is also blocking the removal of the old backend, see bug 1637465 for details. It would be nice if this were to be resolved.

I think the priority/rank of this issue should be increased to reflect that more developers will soon be able to publish extensions on Android: https://blog.mozilla.org/addons/2023/08/10/prepare-your-firefox-desktop-extension-for-the-upcoming-android-release/

I would like to see the priority increased, we would like to decommission some old code (Bug 1637465), and this is a blocker.

(In reply to Simeon Vincent [:dotproto] from comment #6)

I think the priority/rank of this issue should be increased to reflect that more developers will soon be able to publish extensions on Android: https://blog.mozilla.org/addons/2023/08/10/prepare-your-firefox-desktop-extension-for-the-upcoming-android-release/

while this is a great argument, i can't avoid to point out that the star of Firefox extensions: uBlockOrigin, was always allow-listed on android and always made use (or is still broken by) this feature.

(In reply to Mathieu Leplatre [:leplatrem] from comment #7)

I would like to see the priority increased, we would like to decommission some old code (Bug 1637465), and this is a blocker.

Thanks. I will ask the GeckoView team.

Does this bug cover synchronizing stored data across mobile and desktop devices also? Now I'm trying to develop an addon communicating between android and desktop based on storage.sync so this bug looks to be a blocker.

See also https://github.com/mozilla-mobile/fenix/issues/14218.