**SOLVED**
While the main client appears to work fine, the browser extension is useless on my system - nothing happens when clicking the icon in a username field, and when using the right-click menu to fill username and password, again, nothing happens. The database is unlocked and detected as connected, and browser integration is enabled, so I'm at a loss as to what to do to fix it.

edit: autotype works, but this is unrelated to the extension.

edit2: Somehow, it's all working now, one particular site was fixed by removing its subdomain in its entry, but I've no idea why all the others started working - one of the restarts or extension reinstalls must have done the trick

Works really well on Firefox across both Windows and Linux (Fedora 33). Only thing I don't like is that sometimes I can't get the banner to go away or save a new account and password, but I think it's something that's borked with my PC's configs.

I love it. Much more friendly!

As a KeePassXC user, this extension is absolute gold. Getting it to work isn't entirely intuitive. Tips from a happy user:

Make sure the KeePassXC database has permission to link by checking off the relevant boxes under Tools > Settings > Browser Integration and Database Settings > Browser Integration. Don't close KeePassXC. Go to the extension and connect it under Settings > Connected Databases. In order for this extension to function, KeePassXC *must be running*. In KeePassXC, you can choose to minimize or hide the program instead of quitting under Tools > Settings. In the KeePass entry itself, don't forget to specify a URL.

Like it! brings all my passwords together in one place, where I can control them.
TNX Guys for the extension.

Me costó un poco conectarla al principio pero siguiendo la pista de la documentación lo logré en seguida. Una maravilla para la seguridad de nuestras contraseñas!

Edit: It turns out the checkbox for Browser Integration with Firefox/Tor Browser became unchecked for some reason. After rechecking it, it works without a problem.

I've gotten KeepassXC set up on Brave and Vivaldi already. But this Firefox extension just gives me the error: "Key exchange was not successful" when I try to reload the connection.