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

Thank you TonyE...excellent response. Now I will tell the Bank !!!

When you are logged in, please click the Helpful button next to the answer that solved your Firefox support issue.

Thanks TonyE for the pointer to the new designation of a secure connection. Firefox 4 a right pain in the bum at the moment because the lock was a recognised standard security feature and now I find my bank only comes up as a partial encryption ! Just great for online bank management.

Ideally you should focus on the new identity button that is explained in the previous posts.

However, there is an addon that adds the padlock icon to Firefox 4. https://addons.mozilla.org/en-US/firefox/addon/padlock-icon/

Because the status bar at the bottom of the window is no longer shown by default, this addon displays the padlock inside the identity button. For users who are trained to look for a padlock, this might help them to move their attention to the new identity button.