When signing into accounts.firefox.com, I've noticed that the extension is reliably slow to open and autofill does not work.
A few unexpected things here.
Step 4: It's uncharacteristically slow to bring up results. Other sites are done autofilling within ~1/2 second of me hitting the key combo.
Step 5: It shouldn't be popping up to ask me at all, because I only have one Login item associated with this site. The other 3 items are Identity items that don't mention Mozilla or Firefox at all. I only have 3 Identity items total, so I suppose it's surfacing all of them for some reason. I've double-checked that the associated website for the Login item is correct -- it is (verbatim: https://accounts.firefox.com) though it also includes a secondary website (verbatim: https://mozilla.org).
Step 7: There's no indication of why autofill fails. The dialog dismisses itself after I press the button and then... nothing.
I have upward of 200 Login items in 1Password, but this is the only one that exhibits any of these issues.
Here's a screenshot of the Login item in question with all fields visible.
Here's what I get when I try cmd-\.