Digital rights holders can restrict access based on operating system or browser. This leads to contradictory and inconsistent situations. For example, Apple TV allows access with High Sierra and Firefox 115 OSR, but not with Dynasty. My Spanish fiber optic TV provider does the same. SkyShowtime, on the other hand, doesn't allow access with any High Sierra browsers. At a minimum, Chrome 128 and Firefox 140 are required. This is usually stated in the access information, and there are multiple combinations, which is why I congratulated you. With Catalina, all browsers have access to all platforms except Safari on SkyShowtime, which is also blocked. The combinations they use are chosen by the owner and don't depend on the operating system, but rather on combinations they specify.