“…you do not have sufficient privileges…” when updating Firefox

Problem

When you attempt to update Firefox on your Mac by dragging the app into the Applications folder you get the following error:

Solution

1. Keep this window open:
   
2. Double click on the Applications folder to open in..
3. In the Applications folder you will see Firefox. Move it to the Trash.
4. Go back to the window shown in Step 1 and drag the Firefox icon on to the Applications folder icon.