gecko/mobile/android/base/resources/drawable/tabs_tray_bg_repeat.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- This Source Code Form is subject to the terms of the Mozilla Public
   - License, v. 2.0. If a copy of the MPL was not distributed with this
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<bitmap xmlns:android="http://schemas.android.com/apk/res/android"
        android:src="@drawable/tabs_tray_bg"
        android:tileMode="repeat"/>