You should probably not be posting this here. I'd recommend asking the waterfox community directly. That being said, this sounds like an issue being caused by the browsers user agent. There are different methods to change your user agent, I recommend looking up "waterfox change user agent" or similar search terms to find a good solution. Just change the user agent to a default Firefox tag rather than the fork user agent.
Edit: A user agent is just a string of text that tells websites what browser you are using. So currently the site is being told you're using waterfox which it doesn't consider a legitimate browser even though they are both similarly functional. By changing the user agent you are tricking the site into thinking you are using default Firefox or some other browser.
