If you go directly to https://www.firefox.com/download/ios/ there is a button that opens App Store for you. Can you install/update/open from there?

Does the app itself open, and "no longer works", or it is not even installing/opening for you?

Thanks, JBR, With a combination of using my iMac to connect and share data and paying closer attention to the instructions on how to delete the app, I was able to restore a fully functioning app on my iPhone. I really do appreciate the quick response. The part I wasn't paying attention to was the need to temporarily select another browser as the default in order to delete and reinstall Firefox. My bad.