Find the secret codes of your device
If your device has ADB access, with or without debugging, all you need to do is extract the folder containing the pre-installed apps and search for them.
1. Extract the webapps folder from the system
adb pull /system/b2g/webapps
2. Enter the extracted folder
3. Extract all the application.zip files contained in the folder in several folders that we will call "app"
for f in $(find . -type d); do unzip $f/application.zip -d $f/app/; done
4. Run the search filter (but if you want you can configure it for different terms), here for example there are the various correspondences to the sequences between # and * and the numbers from 0 to 9
grep -EIro '[*#]+[0-9]+#[*#]*' .
5. Read inside the file of each path the functions of those codes extracted. Be careful not to type in the codes right away, you may have unwanted effects on your device.
And as Speeduploop would say "Happy hacking!" ;)