Method 1:
  1. Open Firefox
  2. Select View history, saved bookmarks and more icon on the top right  User-added image
  3. Select History
  4. Click Clear Recent History
  5. Select desired Time range to clear
  6. Mark the Cache and Cookies box
  7. Select Clear Now
  8. Close all instances of Firefox and re-open
    • Note: In general, default settings do not need to be changed
Method 2:
  1. Open Firefox
  2. Hold down Ctrl, Shift, and Delete keys simultaneously
    • Note: Clear All History pop-up will appear
  3. Select desired Time range to clear
  4. Mark the Cache and Cookies box
  5. Select Clear Now
  6. Close all instances of Firefox and re-open
    • Note: In general, default settings do not need to be changed
Please see these articles to clear cache and cookies in other browsers:
Clear Cache and Cookies in Google Chrome
Clear Cache and Cookies in Internet Explorer