I’ve been experimenting with Safari Extensions for awhile ( https://github.com/krypted/Word-Replacer-Safari-Extension ) and once we publish them we might need to continue to use an old version for testing. Extension updates can then be deleted by writing a boolean InstallExtensionUpdatesAutomatically key into the com.apple.Safari defaults domain and setting the option to false: defaults write com.apple.Safari InstallExtensionUpdatesAutomatically -bool false To remove the key and simply return to the default state: defaults delete com.apple.Safari InstallExtensionUpdatesAutomatically