Eh, there's actually a lot of website content management systems out there that have difficulties with Firefox compatibility, especially for non-core site components (which a calendar or map graphic interface is likely to be). I can't remember the exact details, but IIRC it's something to do with optimizing for Google and Apple search engines as they control the market, especially Google. The odd part is, to my knowledge, they both use the same backbone kernel (which MS Edge also uses after MS finally gave up on having their own with IE...).
And let's face it, all mainstream browsers are about the same amount of secure, they're really dependent on what settings you use and what data you're willing to share.
So while your frustration is understandable, there's a good chance you're in the minority of browser choice for the park to care enough to do anything about browser compatibility. You're better off switching to one of their recommended browsers and just roll with it.
