Issue 3820 - Selecting Settings within ABB for Android causes the app to crash.

mobile/android/base/resources/values-v21/themes.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/. -->
 
 <resources>
 
     <!--
         Base application theme.
     -->
-    <style name="GeckoBase" parent="@android:style/Theme.Material.Light">
+    <style name="GeckoBase" parent="Theme.AppCompat.Light">
         <item name="android:colorPrimary">@color/text_and_tabs_tray_grey</item>
         <item name="android:colorPrimaryDark">@color/placeholder_active_grey</item>
         <item name="windowActionBar">false</item>
         <item name="android:windowNoTitle">true</item>
         <item name="android:windowContentOverlay">@null</item>
         <item name="android:actionBarStyle">@style/GeckoActionBar</item>
         <item name="android:actionBarTheme">@style/ActionBarTheme</item>
         <!-- TODO (bug 1220863): Once we extend AppCompatActivity, set actionBarStyle. -->
         <item name="android:alertDialogTheme">@style/GeckoAlertDialog</item>
     </style>
 
     <style name="GeckoPreferencesBase" parent="Gecko">
         <item name="android:windowActionBar">true</item>
         <item name="android:windowNoTitle">false</item>
         <item name="android:actionBarStyle">@style/ActionBar.GeckoPreferences</item>
+        <item name="colorPrimary">@color/primary_material_dark</item>

[René Jeschke, 2016/05/17 10:21:13]

Is this line really necessary? Also, this item already appears, with fully
qualified namespace, at the top of the style definition.

[diegocarloslima, 2016/05/17 12:19:53]

This line isn't necessary (in the means of preventing the crash) once we're
setting Theme.AppCompat.Light as parent. I added this for sort of a temporary
styling fix on the action bar background. Without that, the action bar is light
gray with white text and its really hard to read.

Even though the fully qualified name and the compatibility name in the end means
the same thing (i.e. same color attribute), if we use a theme that doesn't
define the compatibility attributes on its hierarchy (i.e.
Theme.Material.Light), we're vulnerable to some crashes like this because of 
weird behaviours of some appcompat stuff. In this particular case, the crash
happens when PreferenceActivity gets inflated and tries to read the colorPrimary
styling attribute (not the android:colorPrimary one), and since it could find it
in the current theme, it throws an exception

     </style>
 
     <style name="GeckoAlertDialog" parent="@android:style/Theme.Material.Light.Dialog.Alert">
         <item name="android:colorAccent">@color/fennec_ui_orange</item>
     </style>
 
     <style name="ActionBar.FxAccountStatusActivity" parent="@android:style/Widget.Material.ActionBar.Solid">
         <item name="android:displayOptions">homeAsUp|showTitle</item>
         <item name="android:titleTextStyle">@style/ActionBarTitleTextStyle</item>
     </style>
 
     <style name="ActionBar.GeckoPreferences" parent="@android:style/Widget.Material.ActionBar.Solid">
         <item name="android:titleTextStyle">@style/ActionBarTitleTextStyle</item>
     </style>
 
     <style name="GeckoAppBase" parent="Gecko">
         <item name="android:actionButtonStyle">@style/GeckoActionBar.Button</item>
         <item name="android:listViewStyle">@style/Widget.ListView</item>
         <item name="android:panelBackground">@drawable/menu_panel_bg</item>
         <item name="android:spinnerDropDownItemStyle">@style/Widget.DropDownItem.Spinner</item>
         <item name="android:spinnerItemStyle">@style/Widget.TextView.SpinnerItem</item>
         <item name="menuItemActionViewStyle">@style/Widget.MenuItemActionView</item>
         <item name="menuItemDefaultStyle">@style/Widget.MenuItemDefault</item>
         <item name="menuItemSecondaryActionBarStyle">@style/Widget.MenuItemSecondaryActionBar</item>
         <item name="tabGridLayoutViewStyle">@style/Widget.TabsGridLayout</item>
     </style>
 
 </resources>