The "there is something wrong with you if you are at all off the beaten path" has cropped up a lot more for me recently; two examples both from 2026:

1. You can't use Firefox with our website (when I got this popup, I thought I had been transported back in time 20 years, but with Chrome substituted for IE).

2. You can't sign up for accounts with an e-mail from a "custom domain"

2a. I ran some tests; it's the domain itself, not the host, so e.g. [email protected] is allowed but not a [email protected], even if hosted by google).

2b. After a bit of back-and-forth with support: "No, we won't tell you the list of allowed domains, but gmail and hotmail both will work."