As Captain America would say "Language" Apple has restrictions on what browser engine can be used on iOS/iPadOS as Firefox is basically a shell wrapper for webkit. Thankfully Apple does not have the same restrictions on macOS. https://support.mozilla.org/en-US/kb/add-ons-firefox-ios The page you tried to install from was for (desktop) Firefox and there is a section for Firefox for Android. However there may be some good news at least for EU users as per https://developer.apple.com/support/alternative-browser-engines/