Problem with accessing Pinterest on Firefox

Pinterest is a social networking site that allows people to "pin" pictures, drawings, recipes, etc. to their own "Boards." On the Pinterest.com webpage, many of such pinnable items are shown with a menu bar including the option to "Repin It" to your Board. When HTTPS 3.1 is enabled for Pinterest, the RepinIt button starts that action but then spins endlessly without doing anything. Disabling HTTPS Everywhere 3.1 for Pinterest in the options section allows the actions to succeed. This has been a major source of concern for Pinterest aficionados.