replaced iMac with Mac Mini, autofill credit card info doesnt work

Try to go to about:config and add your country code to the extensions.formautofill.addresses.supportedCountries preference.

Thanks. The country code is already in. I did find that this line:

extensions.formautofill.creditCards.os-auth.locked.enabled false

is showing as false, but it also shows as locked. I cannot acces it by double tapping. Am I on the right track? If so, how can I unlock this to change it?

WARNING from the moderator team: Changing Firefox preferences from the about:config page can sometimes break Firefox or cause strange behavior. You should only do this if you know what you're doing. Please read Firefox advanced customization and configuration options to learn more.

Is this a version of Firefox you have downloaded and installed from Mozilla?

As far as I know. It has been working fine for me for years until I replaced the iMac last week.

I see your warning and am heeding it. But, it seems like there should be some way for me to get the credit card autofill feature back. Anybody have any suggestions?

This is strange esp. since you have a direct comparison of presumably the same credentials in the same place at the same time. Was the previous Mac also running the same macOS 26 Tahoma already before, or something older?

(The pref is for protecting the autofill with e.g. system biometrics so there's no need to fiddle with it, you can change it just from settings if need be.)

Is it happening on all sites, or just a specific one? (Would you mind sharing your country, as the autofill logic differs e.g. between US and UK…)

You can try autofilling some of Mozilla's testing forms to see if at least these work as expected:

If you open https://mozilla.github.io/form-fill-examples/ there's several variants in the top "Forms" section — if you click through the links, some will have credit card fields to test. This is just a dead form that will not pay for anything or send the data anywhere;) it's only for Mozilla testing to see how different types of forms handle the autofill input. It also includes some very simple forms to verify your autofill even works on these. Basically all of that is used in Firefox testing, so these are believed to be working with your credentials — if not, there's something off, because these "should just work".

These forms are safe and do not send your data anywhere, everything stays just in your browser, there's no "server" component that would be able to listen, these fields are statically served and only used for heuristics and testing. (If you don't feel like autofilling your real card, you can add a "4242424242424242" Visa with any future expiration to your payment methods for testing.)