GO:LIVECAST: Even if I set Facebook's privacy setting to "public," the webcast is limited to my friends.

It might be that the initial login settings failed.
Access Facebook from your computer's browser, and check the settings.

Log in to your Facebook account.
Open the “Settings” screen, then click “Apps and Websites” on the left.
Click “View and edit” of the GO:LIVECAST.
Update the information you're sharing with the app, who can see that you use the app and notifications you receive, then click the “Save” button.