According to the help article referenced below, it could be asking for your system password: <blockquote>'''Require authentication for autofill''' To add further protection, you can select to require authentication before autofilling the credit card information. This requires your operating system password (or authenticate using your fingerprint, face, or voice login, if enabled) this is usually the password used to unlock your computer. Please note, this is <strong>not</strong> your Mozilla account password. <ol><li>In the Menu bar at the top of the screen, click Firefox and then select Preferences or Settings, depending on your macOS version.</li> <li>Click the Privacy &amp; Security panel and scroll down to the ''Autofill'' section.</li> <li>Click the checkbox next to <strong>Require macOS authentication to fill and edit payment methods</strong> to turn it on, or uncheck the box to turn it off.</li></ol></blockquote> Ref. [[Automatically fill in credit card and payment method data on Web forms]]