Save what you typed
You do not have to type a profile from scratch. If the form on screen is already filled, Save from page copies those values into the selected profile.
Save from page
Open the popup on that tab and press Save from page. Choose the current profile or a new one. Only values the extension can match are stored. The status line reports how many were saved. A page with nothing new reports that too.
Offer to save
In settings, the offer-to-save option can ask after you type on a site. You pick an existing profile or start a new one. You can ignore the card. The values are not uploaded either way.
Sites you want left alone
Add a site exception when a host should not be filled or should not prompt. Remove the exception later from the same list.