If your browser is sandboxed with Snap or Flatpak, this extension does not work. It's not fixable as the required integration breaks the sandbox and so won't be allowed. If you have a browser installed on your host computer (i.e. native, not sandboxed) then there is no problem with this extension. But since Firefox is now ONLY supplied as Flatpak or Snaps on Ubuntu, this effectively locks out all Linux users from using KeepassXC.

> his has nothing to do with the extension itself, but Snap/Flatpak implementation of the browser itself.

But it has everything to do with the extension. It is designed in a way that is simply incompatible with the security model of a sandboxed browser. Nothing about the sandbox is "broken", the kind of code execution required by the extension and the server is what a sandbox is designed to prevent. This is exactly what a malicious extension would do to break out of the sandbox. The team should be working on this, or else users will just abandon the project. I'm certainly not going to try to convince Ubuntu that Snap is broken on your behalf, I'm just going to install something else that works.