The padlock has been replaced by the site identity button, for details on using it see https://support.mozilla.com/kb/Site+Identity+Button

Thanks Tony - a great help!

You're welcome

Site identity is fine; it confirms I am where I think I am. The padlock is a global standard for a secure connection. Please bring it back.

The padlock icon is still present, it shows when you click on the site identity. In my opinion, color-coded site identity may be even better than that, as it provides more information about site you're visiting.

You can look at this extension:

• Padlock: https://addons.mozilla.org/firefox/addon/padlock-icon/