Hello! The statement "Mozilla Firefox 66 and 'earlier versions" is not ambiguous at all, and your first thought that the meaning of "versions prior to 66 (65, 64. I think the developer of the app forgot to update the text to 72, which caused this misunderstanding.
I can see where the misunderstanding happened because if you are using Firefox 72, but the app say it "supports 66 and earlier version" then the app shouldn't work with the latest Firefox version.