Waterfox Classic is based on 6 years old Firefox.
So I can imagine a lot of new API is missing (as well as security patches).
These days even Firefox ESR based on Firefox 102 is sometimes “too old” for modern websites, and it’s not even one year old!
Anyway, using Waterfox classic can be dangerous, any malicious website can easily check what browser are you using and check the database for the known vulnerabilities and then serve you one - ideally some that doesn’t require user interaction.