Following these instructions, you'll be able to successfully clear your browser cache and cookies.
- Click the menu button and select Options.
- Select the Privacy & Security panel.
- In the Cookies and Site Data section, click "Clear Data…".
- Remove the check mark in front of Cookies and Site Data.
- With Cached Web Content check marked, click the Clear button.
- Close the about:preferences page. Any changes you've made will automatically be saved.