This behavior just started a few days ago for me. I’ve been using Bitwarden and FireFox windows for years, and this just started. When I use BW to fill-in the username/password, then hit login, BW offers to update existing login. It’s getting quite annoying.
When I turn off “Ask to update existing login”, the unwanted behavior stops. As this is something that started relative recently for me, I wonder if it was a result of recent auto-update. If there is anything I can post to help resolve this, please let me know.