Likely the extension failed to load after installation from MAS. This can be verified with:
pluginkit -mAvvv -p com.apple.Safari.extension
Sometimes rebooting or quitting both the app and Safari then relaunching is sufficient to trigger loading the extension. Otherwise quit Safari, trash the application and reinstall from MAS.
Likely the extension failed to load after installation from MAS. This can be verified with:
Sometimes rebooting or quitting both the app and Safari then relaunching is sufficient to trigger loading the extension. Otherwise quit Safari, trash the application and reinstall from MAS.