With pleasure 
Not sure if I understand what you mean by “interaction is desired but not autofill” … like with the Passbolt’s dropdown ? Maybe with this type of auth, it could be “real” autofill, because there is no (or at least less) risk for the password to get “stolen” by iFrame ; and there is no need to find the login form because there is a function to provide login to the page protected by basic auth.
From the doc, the extension has to be careful not to enter an infinite loop if bad credentials are provided, but it can have a many tries.
Or you mean it has to be a first bad try, so the listener get ready ?
Sorry for my confused answer, I don’t really get the meaning of your message 