If you have tried Firefox in windows you have noticed that the ubuntu Firefox does not use backspace to go to the previous page you can change this by doing the following :

1- open you firefox browser.
2- in the address type about:config
it will give you a notification message click i'll be carefull, i promise!
3- type backspace and press enter key.
4- the search result will be : browser.backspace_action click on it and change it's value to 0 (zero)

and you are done now enjoy the backspace.