In case you are working with Safari and you don’t see the 1Password Plugin after installation in extensions, do the following:

1. Close Safari

2. Open a terminal

3. Execute the following in the terminal:

/System/Library/Frameworks/CoreServices.framework/Frameworks/LaunchServices.framework/Support/lsregister -f -R /Applications/Safari.app

4. Restart Safari

5. The 1Password extension is now working.