src: http://lifehacker.com/269945/set-backspaces-firefox-behavior

The backspace key performs differently in Firefox on Linux than on Windows or Mac. On Windows and Mac, hitting the backspace key will navigate the ‘fox back one page. In Linux, hitting backspace will scroll your current page up (shift+backspace will scroll your current page down). This is pretty annoying for dual-booters who expect the backspace key to do the same thing across all partitions. The Ubuntu on Dell Inspiron 1501 weblog explains how you can customize your backspace key in about:config.

Set "browser.backspace_action" to either 0 or 1
0 – Pressing backspace button will go back a page in the session history
1 – Pressing backspace button will scroll up a page in the current document and
[Shift]+[Backspace] will scroll down.

囧，哥终于找到怎么在linux下面让firefox 按退格键 后退了