Firefox will display a lock icon with red strike-through in the address bar, when a login page you’re viewing does not have a secure connection. If you enter a password on such pages, eavesdroppers or attackers could steal it.
You will also see a warning message when you click inside the login box to enter a username or password.
Note: When you start entering your login information, the warning message can obscure the password entry box. To dismiss the warning, either press the Tab key or click on the page background after you type in your username.
What can I do if a login page is insecure?
If the login page is insecure, check if a secure version exists by adding https:// in front of the website address. You can also contact the website administrator and ask them to secure the connection.
- The image "https_secure_lock_gree n_icon" does not exist.
About insecure pages
Pages that need to transmit private information, such as credit cards, personal information and passwords, need to have a secure connection to help prevent attackers from stealing your information. (Tip: A secure connection will have "HTTPS" in the address bar, along with a green lock icon"HTTPS" in the address bar, along with a gray lock icon.)
Pages that don’t transmit any private information can have an unencrypted connection (HTTP). But, it is advised not to enter private information, such as passwords. The information you enter can be stolen over this insecure connection.
Note for developers
For developers looking to learn more about this warning, please see this page. The page explains when and why Firefox shows this warning, and will also provide some details on how to fix the issue. For more information, see this blog post and this Site Compatibility document.