DeltaSync — KeePass search & go by DeltaSync

This add-on is the browser half of DeltaSync, a GPL-3.0 KeePass sync tool. It cannot read any database itself.
It talks over native messaging to dk.hbb.keepass_deltasync, which is a subcommand of the separately installed keepass-deltasync binary. The host reads the user's local .kdbx via keepassxc-cli and returns only an entry's uuid, title, URLs and group path — enforced as an explicit allow-list in the host, so no field beyond that can be sent. No passwords, usernames, notes or attachments ever reach the browser, and the masterpassword is read by the host from the OS keyring rather than passing through Firefox.

The add-on requests no host permissions and runs no content scripts. Its only action is tabs.update/tabs.create to an http(s) URL taken from the user's own database.

Source (unminified, no build step) and the protocol design:
https://gitlab.com/Star95/keepass-deltasync — see docs/browser-extension.md and client/cmd/keepass-deltasync/browser_index.go.