If you have upgraded your 1Password app for macOS to version 8 and installed its extension but you can not see it in Extensions list, then try this resolution.
- Quit Safari
- Open Terminal
- Paste in this command
/System/Library/Frameworks/CoreServices.framework/Frameworks/LaunchServices.framework/Support/lsregister -f -R /Applications/Safari.app
- Reopen Safari
- 1Password for Safari must be in Extensions tab of Safari Preferences