Early days, but very pleased to find it works well with Firefox 55.0.2 (64-bit) on my Ubuntu install (17.10 beta). This now means I can move across to KeepassXC instead of Keepass2 with Mono. The only issue I had was making sure that the KeepassHTTPServer was running in KeepassXC (remember to restart); without doing this you can't connect! It is also nice to be able to manually approve access to a password rather than just blindly fill (if you want to).