This tutorial is for Cherry Mobile Ace Firefox OS.....
Hard resetting / factory resetting your phone will solve the following issues:
1. If you forgot your password
2. System Instability
NOTE: Performing hard reset will erase your data.
To hard reset:
1. Turn off your phone
2. Press and Hold Volume UP + Power Button simultaneously.
3. Release the buttons when you see the Ace logo and wait until the phone power up.
4. Herese trick. If your phone has password, slide to unlock first then you will see MMI test on your screen.
5. Tap Restore Factory Settings -- Then tap RESET
6. Your phone will automatically REBOOT.
Here is a video tutorial
I hope this tutorial helps you.. If you have any question just drop a comment.