This usually happens when a website does not correctly detect the browser version. Even though you are using Firefox, the site may be reading the user agent incorrectly or treating it as unsupported. Try updating Firefox to the latest version and disabling any user-agent-changing extensions. Clearing the cache and cookies for that site can also help. If it still appears, it is likely a website-side detection issue, not a problem with your browser.

Firefox is basically a shell for webkit on iOS/iPadOS which is also why there are no extensions like there are for Android and desktop Firefox. https://support.mozilla.org/en-US/kb/add-ons-firefox-ios