[Backspace]キーで戻る機能を廃止した「Google Chrome 52」がベータ版に - 窓の杜を読んで、Firefox はどうなっているのか?

キーボードショートカット | Firefox ヘルプ

Firefox: バックスペースの動作 - えむもじら

user_pref("browser.backspace_action", 2);

Possible values and their effects

Pressing [Backspace] will go back a page in the session history and [Shift]+[Backspace] will go forward. (Default in Windows)

Pressing [Backspace] will scroll up a page in the current document and [Shift]+[Backspace] will scroll down. (Default in Linux builds before 2006-12-07)

Any other integer value will simply unmap the backspace key. In Linux builds after 2006-12-07, the default is 2.

ソース:Browser.backspace action - MozillaZine Knowledge Base