Installing or uninstalling extensions, and turning them on or off, may take effect immediately or after you go to a new web page or refresh the current web page.
Important: The first time you open Safari, you get warnings about extensions that slow down browsing or are no longer supported:
Extensions that slow down browsing: The extensions are turned off. You can turn on the extensions in Safari settings.
Developer-signed .safariextz-style (legacy) extensions: The extensions don’t load and no longer appear in Safari settings. You can’t turn them on.