How to toggle calendar.google.enableEmailInvitations to true in Thunderbird?

Within the context of the Accept and Decline button missing in thunderbird when receiving an invitation where an answer in part explains:

Using the config editor, simply set calendar.google.enableEmailInvitations to true. You may also want to set calendar.google.sendEventNotifications to false to avoid the possibility of an old bug that sent new events instead of notifications; I've not tested this. Then, restart thunderbird.

How is calendar.google.enableEmailInvitations toggled to true?

There should be an option to open Preferences and then select "advanced" which was either changed, from when the question was asked, or I'm simply not seeing it.