Are you using a fork of Firefox like , Waterfox , or a Linux distro-specific build?
If the box above is checked but streaming sites still aren't working, verify the plugin is actually installed: firefox widevine plugin
Firefox updates Widevine automatically, but you can force check: Are you using a fork of Firefox like
The Firefox Widevine plugin is typically installed automatically by Firefox when a user attempts to play Widevine-protected content for the first time. The plugin can also be updated automatically by Firefox to ensure that users have the latest security patches and features. firefox widevine plugin