I continue to see issues with password managers from what you noted to "it doesn't work with a site I use."
So a few thoughts.
1. https://support.mozilla.org/en-US/questions/1185793
Install a version, turn off updates.
2. https://addons.mozilla.org/en-US/firefox/addon/roboform/?src=recommended
Install the addons and if buggy, report the bugs or they won't know or fix.
I've subscribed to RoboForm for a few years now but there seems to be a problem working with web browsers that can remember your password.
I heavily use passwords both on my computers and my cellphone and have RoboForm everywhere. It seems more frequent that a site will say that I've changed my password recently, and I often have to because either RoboForm has a different password or the browser has. I waste time changing the password but it often doesn't get transferred over to RoboForm or the browsers.
I'd address this with RoboForm but I'm open to other password programs if they have this issue solved.