Convenient extension but $4.99 per month is a steal. Disabling the extension without notice with the only option for a monthly subscription is dishonest.
As already recommended by other users, download the free version web.archive.org/web/20240524062951/https://addons.mozilla.org/firefox/downloads/file/4233940/autofill_quantum-11.9.0.xpi and disable automatic updating.

When the developer returns to the real world I am also willing to spend a few $ to contribute to the development.