Have you checked this guide: https://support.mozilla.org/en-US/kb/control-whether-firefox-automatically-fills-forms ?

It should allow you to troubleshoot this. Otherwise, it might also needs to be changed directly from the iOS settings, not only from Mozilla.

How do I get to the IOS Settings? I went to preferences and cannot find any topic within the preferences. Thanks in advance Perry

You'll have to save your payment details from Settings > click your name > Payment and Shipping. This should make it official that you have that as personal information.

Have you also looked into this article: https://support.mozilla.org/en-US/kb/firefox-doesnt-save-web-form-entries ?