See the screenshot, is simple :)

Thank you (grazi ??), that's what I was looking for... However, two comments to Mozilla developers:

1) It would be clearer to expand this choice to never save the password for a site to read: "Never save FOR THIS SITE"

2) Can this selection be placed in the initial pop up box as a check-box choice, and not as a drop-down pick choice?

You could also add any particular site in :

Options => Privacy & Security => Browser Privacy

Under 'Forms & Passwords' => Exceptions

See screenshot :

I'm aware of that option, but it's pretty deep in menus for most users.

I believe in the past there was a checkbox choice in the popup "do you want to remember password", and having a checkbox there to add the specific site to the exceptions list would probably be most user friendly.

asap8298 said

I'm aware of that option, but it's pretty deep in menus for most users. I believe in the past there was a checkbox choice in the popup "do you want to remember password", and having a checkbox there to add the specific site to the exceptions list would probably be most user friendly.

That might have been enabled in the past or maybe not so without knowing whom installed and configured it in the past that is all hearsay right now. User should be learning about their Browser and be security savvy nowdays and to not know Browser security isn't a excuse to not learn about it. Most if not many of these can be searched see how it is done.

There should be an arrow present between the two buttons (Don't Save and Save) in the doorhanger that opens under the Key icon on the location/address bar. If you click this arrow then you see the "Never Save" choice.