To change passcode on your Firefox OS running device, follow these steps.

Step 1: From homescreen tap on Settings.

Step 2: Tap on Screen Lock under Privacy and Security section.

Step 3: To change passcode, tap on change passcode, enter your old passcode and enter your new passcode to change it.

In case if you want to turn off password lock on your Firefox OS running device then just turn off Passcode lock under Lock screen.

By following, the above steps you can password lock your Firefox OS running smartphone and can save it from unauthorised access.