1. Click on the Tools bar.
  2. Click on Options (On Mac, it's labeled Preferences).
  3. On the menu to the left, select Privacy & Security.
  4. Under the Cookies and Site Data option, click the "Clear Data..." button.

     
  5. Select only the two options and hit clear now.

     
  6. If on a Windows computer, close and re-open Firefox to save your changes. If on an Apple computer, go to the Firefox menu on the top menu bar and select Quit for the changes to take effect.