In Firefox on Ubuntu, I noticed that pressing the Backspace key does not go back to the Previous page. (An alternative is to use Alt+←) However, this used to work fine on Windows and is an intuitive keyboard shortcut to use for this operation.
To configure Firefox to make Backspace go to the Previous page type in
about:config in the Location Bar and look for the
browser.backspace_action entry. The value will be either 1 or a value greater than 1. Set it to 0.
Reference: Browser.backspace_action at MozillaZine