For the most part, this functions ok and I'm able to use it. Unfortunately, for some sites (such as https://cards.barclaycardus.com/) it just doesn't seem to detect the un/pw fields even after I manually select them. Barclay's site is particularly strange. When I "choose custom login fields" I get two of the "overlays" for choosing fields. I have issues on Community America Credit Union's site as well, which might have something to do with the fact that the login form "pops open" when you click in the username field. I haven't really had any issues connecting to my KP database, mostly just issues with the auto-fill/field detection. Thanks for the all the hard work though, I appreciate it. I'm sure over time these kinks will get ironed out.
EDIT: PopOS! 18.04 (so ubuntu 18.04) & Firefox 69.0.1