- I'll start submitting beta versions on AMO (say at v0.x.y)
- Until Mozilla reviews it, I'll keep it in beta
- If it passes Mozilla's review, I'll call it stable (v1.0.0 will be functionally identical to v0.x.y)
- If it gets rejected, I'll keep it in beta and continue working on v0.x.(y+1)
Edit: It turns out about three years ago reviews for Thunderbird add‑ons became automated and no longer require human review unless the add‑on uses experiments (wrapped legacy APIs) or handles sensitive data such as address books, which we don't. I'll try submitting the add‑on.
Edit^2: It passed without any intervention. 🎉 I think I'll keep this issue open until the add‑on is reviewed manually or remains in the "Approved" status on AMO for about half a year.

Edit: It turns out about three years ago reviews for Thunderbird add‑ons became automated and no longer require human review unless the add‑on uses experiments (wrapped legacy APIs) or handles sensitive data such as address books, which we don't. I'll try submitting the add‑on.
Edit^2: It passed without any intervention. 🎉 I think I'll keep this issue open until the add‑on is reviewed manually or remains in the "Approved" status on AMO for about half a year.