Force-Kill Apps With the Back Button In Android

In Settings > Applications > Development, there’s an option called “Stop app via long-

press”, which, when checked, allows you to force-kill the current foreground application 

by long-pressing the back button. Useful if you frequently use an app that’s a bit flaky, 

but watch out: some apps use a long-press of the back button as a shortcut for another 

feature (for example, it shows the History in the default browser).