Hi Mary Lou, for iOS devices, you normally install directly from the Apple App Store instead of downloading from a website. Does the App Store method work on your iPad?

To install Firefox in iPhone/iPad (iOS/iPadOS) you have install from Apple App store. The current Firefox on App store requires iOS 15.0 or later at minimum to install and use.

https://support.mozilla.org/en-US/kb/install-firefox-your-ipad-iphone-or-ipod

Note the Firefox version from mozilla.org like say https://www.mozilla.org/firefox/all/#product-desktop-release is for Windows, Linux and macOS as there is no desktop version for iOS/iPadOS.