The login/password is almost never auto-filled by this extension in websites login/password fields. It works only on a very few sites (like Paypal for example).
I tried with the snap version, and the ppa version of KeepassXC, I got the latest version of it, ran the script when needed, nothing worked.

Keepass2 with Kee extension works perfectly on every webpage, so I went back to it. Shame because the installation of keepass2 with mono on linux is a pain, compared to the simple snap install of KeepassXC.

Definitely a little buggy, unlike the main app. Once had an issue where the banner for updating an entry showed up despite the credentials not differing, the banner failed to appear on the next page despite being set to appear after infinite redirects, then on my next login on a different website I was notified that my database had changed despite me not interacting with the banner or database, I said to discard changes, after which the main app froze. Restarting the app usually fixes things, and when the extension works it works well.

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