Exactly. A browser's job as the user's agent is to do what the user wants it to do. It's not an ABI. If an end-user's browser is configured to do something you, as a developer, don't want or expect, and that breakage causes the loss of a sale, it's kind of on you: Either take a principled stand about "what browsers should be doing" and accept the lost sale, or try/catch around non-critical code to make your site more robust to the user's configuration choices.