This guide has been written originally by Ivan Alex HC
This hack is safe meaning no changes are made to
/systempartition and changes are reverted back after factory reset or after an OTA update
system.gaiamobile.org applications folder from the system:adb pull /system/b2g/webapps/system.gaiamobile.org
Now that you have tha application.zip file, you can act in two different ways:
2a. Replace the STARTUP sound (normally the path is /resources/sounds) with the custom one (it can be a mp3 or an ogg file, depends on the device).
2b. Add your audio file in /resources/sounds (or in another path if your startup sound is into a different folder) and go replace it in /js/init_logo_handler.js (normally this file is responsable of the startup processes).
/data/local/webapps using a temporary root accessadb push system.gaiamobile.org /data/local/webapps
adb pull /data/local/webapps/webapps.json
And change the value of the system.gaiamobile.org app
basePath: /system/b2g/webapps,in this way
basePath: /data/local/webapps,Use the JSONLint website to verify that the format is correct for any json file you want to modify.
webapps.json file in its place and reboot the phone:adb push webapps.json /data/local/webapps/
adb reboot
After rebooting you can finally enjoy your custom startup sound.