If you can't remember the login/pswd no one here has access to them as this is just a user help forum only. Sync isn't a backup system as those data was on the main computer and if those are gone then the data is gone as well.

I am not asking if anyone here knows my user and pswd. I am looking to share the saved passwords on my (automatically) functioning phone version of Firefox to my new computer... but can't be sure of my user, and don't know the password. I have just learned that it is possible to request a password reset on the functioning device, and then use that new password to login on the new device. Problem with that, I'm learning, is that the password reset, deletes all stored data from Mozilla server. They say though, that it doesn't effect what is stored on your device. I think I understood the right. (If that's not so, and all data is deleted on the current device, too, then I'm screwed.) If data is uneffected on my phone, then maybe my only option is to request that password reset, and continue to refer to my phone for site passwords when on my computer...until all sites are resaved.

Oh, it is apparently impossible to save stored passwords to .cvs when using the mobile version !!! If it were possible, I'd be almost home.

I don't think there is any convenient solution here, only inconvenient ones.

Is it possible you had any iCloud backups of your old Firefox data from either of your Macs?

I'm not that tech savvy. But, I suspect nothing within a few years as I purchased an outboard SSD back then and relied on Time Machine for backups. If I activated some cloud storage, it would have either been by accident, or done long ago and forgotten.  :(