I'm not sure if this is possible, but I noticed an area where 1Password might be able to excel because of it's embedded activation. If the password manager is activated on the window, it makes sense that it would only be able to suggest for the domain of the window. However, with 1Password X being activated in the input, it seems like it would be able to suggest passwords for the domain of an input inside an iframe.
The example here is an embedded login form for my school website. The window is on umich.instructure.com, but I want to fill an input inside a frame on weblogin.umich.edu.
In this screenshot, 1Password identifies the login form on weblogin.umich.edu and suggests the proper login:
In this screenshot, the login form is inside an iframe. While the domain the form is hosted on is still the same, 1Password uses the domain of the outer window to suggest. I don't have umich.instructure.com configured as a website for this login, so it is not presented.
Does this seem like a possible scenario to address?
In the meantime, I've added the outer domain to the list of websites for this login, so I guess this idea is pretty low priority as well.
1Password Version: Not Provided
Extension Version: Firefox 1.6.3
OS Version: Ubuntu 17.10
Sync Type: Not Provided