Fix Firefox backspace to take you to the previous page

Source: http://embraceubuntu.com/2006/12/21/fix-firefox-backspace-to-take-you-to-the-previous-page/

Type “about:config” in the address bar of Firefox and press Enter.
`Filter` (Ctrl+F) for ‘browser.backspace_action’ and change its value to 0 (zero).