Their website is SO SO bad. It is almost like they don't want you to easily be able to see your bill and investigate the rates. The only part of the website that is easy is making payments.
Every single ISP does this. Even both of Googles ISP brands do it. I've convinced myself it's to hide their coverage maps, forcing you to give address and get a single data point. In reality it just means I never wind up helping friends move ISPs because it feels.lile an abusive relationship no matter what move you make.
It's more that they don't care if, say, an automated support chatbot doesn't work in Firefox. In which case they tell you to just use Chrome rather than submit a ticket telling one of their web devs to fix something.
It's more a case of they don't bother testing using firefox. It may incidentally work on firefox, as a side effect of being tested in browsers that people still commonly use in the 2020s.