Mouseover the
boxes to see each step!Step 1
Click on the 
button at the top left corner of the browser and select 
from the 
menu.Step 2
Click on the 
button.Step 3
Confirm you want to reset Firefox by clicking on the 
button.Step 4
Upon completing the reset, Firefox will display this last message asking you if you want to make Firefox your "default" or main browser.