Piigeon checks whether Web sites protect your passwords and other personal information as you browse the Web. Piigeon indicates this information to you as an icon so that you can decide whether you would like to use a site on your current network.
Here is what the developer has to say about the add-on:
Piigeon monitors whether Web sites protect your username and password when you sign in. For most sites, the cursor will change, telling you whether your password is encrypted or if it could instead be intercepted. Over time a report of your password safety is created. Piigeon also suggests whether you should change your passwords based on how your passwords are shared across sites.
You can find out more about Piigeon from the Firefox Add-on website.