Modify contents in omni.ja, under dom/ path in gecko. Credits to @mcjimenez

fastOmniJA.sh

#!/bin/sh

if [ $# -ne 2 ]
then
  echo "Usage: `basename $0` /path/to/your/gecko/objdir DOM-component(push, apps…)"
  exit $E_BADARGS
fi

DIR_SRC="$1"
DIR_SRC1="$DIR_SRC/dom/$2"

cd ${DIR_SRC1}
make

cd ${DIR_SRC}
make package

OMNI_JA_PATH=/system/b2g
OMNI_JA=omni.ja

SRC_F=${DIR_SRC}/dist/b2g/omni.ja

adb shell stop b2g
adb remount
adb push ${SRC_F} ${OMNI_JA_PATH}/${OMNI_JA}
adb logcat -c
adb shell start b2g