Mozilla Firefox: Empty cache and cookies

Step 1:

In the browser menu, click on the Open application menu icon in the top right-hand corner.

Step 2:

Select Settings.

Step 3:

Under Privacy & Security, go to Cookies and Site data and click on Clear data....

Step 4:

Select under When: the time period from which the data should be deleted. If you want to clear the browser cache, select the option Temporary cached files and pages. If you want to delete the cookies, select Cookies and site data. Both options can also be selected. Click on Clear and the selected data will be deleted immediately.