The Firefox for iOS currently requires iOS 15.0 at minimum to run now since 120.0. It was iOS 14 at minimum during 112.0 to 119.0. The last Release to require iOS 13.0 at minimum was 111.0 https://www.mozilla.org/firefox/ios/126.0/system-requirements/ https://www.mozilla.org/firefox/ios/120.0/system-requirements/ https://www.mozilla.org/firefox/ios/119.0/system-requirements/ https://www.mozilla.org/firefox/ios/112.0/system-requirements/ https://www.mozilla.org/firefox/ios/111.0/system-requirements/ Perhaps if you have a old version that still supported iOS 12.x in Apple ID > Purchase History on the iPad then you may be able to install the older version. I have a old iPad mini 2nd gen with iOS 12.5.7, however since it never had a version of Firefox installed with the ID, I cannot try to see if installing a old version of Firefox from purchase history works.