Was really looking forward to trying this out, but I can't seem to get it to work at all.

Tested with FF 64.0 Portable, KP XC 2.3.4 Portable, and followed directions at https://keepassxc.org/docs/keepassxc-browser-migration/ , but cannot seem to get the browser to connect to the DB. Per the instructions, I've enabled browser integration for FF, but receive the following Error from the plug-in: "Cannot encrypt message or public key not found. Is native messaging or support for your browser enabled in KeePassXC?". Reload button doesn't help, nor does restarting the apps.

EDIT:
Thanks for responding. It sounds as if I need to make some changes to the FF launcher's ini file (in order to get FF Portable to work with this), but it's unclear what those changes are. After searching around a bit more, I see that others are experiencing this problem as well:
https://portableapps.com/node/57907
https://github.com/keepassxreboot/keepassxc/issues/1817

I saw some information at https://github.com/keepassxreboot/keepassxc/issues/1559#issuecomment-369508900 regarding what registry entries need to be shared, but it's unclear to me exactly what steps I need to take to get FF Portable to work with KeePass-XC portable. Could you provide a bit more information about exactly what .ini files I need to edit and with what changes?

EDIT 2: Another user commented that disabling the proxy (Tools > Settings > Browser integration > Advanced) solved the integration issues. I've tried this, and it seems to be a good workaround. The downside is that a second copy of KeePass XC launches with the proxy disabled, but at least it seems to work.