Looks like Firefox prevents Plugins to type in the sync login page (https://accounts.firefox.com/signin?service=sync&action=email&context=fx_desktop_v3&entrypoint=multi-account-containers&utm_source=addon&utm_medium=panel&utm_campaign=container-sync)
I'm not sure since when but definitely since the login re-design.
As a workaround it is possible to use the type-in-window feature or the new drag-to-type feature
So my question is, could this even be fixed, if it is a bug?
1P definitely tries to type in the box (or somewhere else on the page), as I'm seeing this in the debug log:
20384 5170.336 INFO opw_app::api:707 > FillKey is used to fill in firefox browser.
As I'm using an standalone key I'm using the "normal" 1Password extension
currently used Firefox Version: 73.0.1 (but exists in all modern Firefox versions with this login page)
1Password Version: 7.4.751
Extension Version: 220.127.116.11
OS Version: Windows 10 1909 18363.657
Sync Type: Dropbox