gecko-dev/mobile/android/base/resources/drawable/action_bar_button.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
   - file, You can obtain one at http://mozilla.org/MPL/2.0/. -->

<selector xmlns:android="http://schemas.android.com/apk/res/android">

    <item android:state_pressed="true"
          android:state_enabled="true">
        <shape>
            <solid android:color="@color/highlight" />
        </shape>
    </item>

    <item android:state_focused="true"
          android:state_pressed="false">
        <shape>
            <solid android:color="@color/highlight_focused" />
        </shape>
    </item>

    <item android:drawable="@android:color/transparent"/>

</selector>