In Mozilla Firefox, if you press "Backspace" key it works like the Back button and goes back to the previous page you visited.

Although its a useful feature, some people find it quite annoying for following reasons:

• Sometimes people press Backspace key to remove typed characters from addressbar or from a text field but the field doesn't get activated and the browser goes back to the previous page in history.
• This action has been designed to put consistency in Firefox behavior and other Windows applications. In Linux, the "Backspace" key scrolls up in a page. So you might want to get the same behavior in Windows as well.

If you also find it irritating and want to disable or customize behavior of "Backspace" key in Mozilla Firefox, this tutorial will help you.

1. Open Firefox and type about:config in the addressbar and press Enter. It’ll confirm, click on I’ll be careful, I promise! button.

2. Now type backspace in the Filter box and look for following key:

browser.backspace_action

3. The entry "browser.backspace_action" would be set to 0. You can change its value to any of following based upon your requirements:

1 - To change its action to scroll up in a page. You can use "Shift+Backspace" to scroll down.
2 - To disable it.

4. That's it. If in future, you want to restore the action, simply change its value to 0 or right-click on the key and select "Reset".