I've been using this plugin with both KeePassXC and KeePass (via a fork of the natmsg agent) and it works great. Occasionally loses connectivity, but that's usually only after I've had the program up for weeks and due to high load on my workstation which causes. If that happens to you just restart the natmsg processes and all is well again!

Was a little bit difficult to understand how to use it for Mozilla account:
Find it in https://support.mozilla.org/en-US/questions/1276862:
Create a Keepass entry for Firefox and highlight it in the list
From the menu bar select [Entries->TOTP->Set up TOTP...]
Display the QR code in the FF set up web page and copy to the [Secret Key:] field from above.
Accept defaults and press [OK]
From the menu bar select [Entries->TOTP->Show TOTP..].
copy this number into the response field in the FF set up web page

It should now be all set up.
To use highlight the entry and select [Entries->TOTP->Show TOTP... ](or copy TOTP... if easier)

Excellent module

Overall, the browser integration for KeePassXC works well. Sometimes there are some issues with autofill when the site has you enter a username, then a password on the next page, but overall it works pretty well.

Works only for a part of sites. For all others just can't fill in credentials. Also when creating a new account a pop-up bar displayed to store new data. But click in it produces error "can't save credentials". Meanwhile the database is connected and unlocked.
So I decide the plugin to be quite buggy.

works perfectly !

Unintuitive to complete uselessness