RETURN TO MAIN ARTICLE Clear all cookies and the cache
If deleting cookies for the site with the problem did not fix the error, clear all the cookies stored on your computer and clear the Firefox cache:
- Click the Library button
on your toolbar. (If you don't see it there, click the menu button 
then click .) - Click and select .
- In the Time Range to clear: drop-down, select Everything.
- Below the drop-down menu, select both Cookies and Cache. Make sure other items you want to keep are not selected.
- Click .