After installing the test version 1Passwort V7 the extension for Firefox with 1Passwort V4 is no longer executable. Deinstallation and reinstallation of the extension and of Firefox, as well as computer restart brought no success Windows 10 Firefox 65 (64bit).
Edit: I Found the solution myself in the Forum
"You will also need to have Native Messaging enabled in 1Password Help > Advanced in order for them to connect. Let me know how it goes."