--- a/build.gradle
+++ b/build.gradle
@@ -46,16 +46,17 @@ buildscript {
         }
         // For in tree plugins.
         maven {
             url "file://${gradle.mozconfig.topsrcdir}/mobile/android/gradle/m2repo"
         }
     }
 
     ext.kotlin_version = '1.1.51'
+    ext.support_library_version = '23.4.0'
 
     dependencies {
         classpath 'com.android.tools.build:gradle:3.0.1'
         classpath 'com.getkeepsafe.dexcount:dexcount-gradle-plugin:0.8.2'
         classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
     }
 }
 

--- a/mobile/android/app/build.gradle
+++ b/mobile/android/app/build.gradle
@@ -208,26 +208,26 @@ android {
             // we have tests that start test servers and the bound ports
             // collide.  We'll fix this soon to have much faster test cycles.
             maxParallelForks 1
         }
     }
 }
 
 dependencies {
-    implementation "com.android.support:support-v4:${mozconfig.substs.ANDROID_SUPPORT_LIBRARY_VERSION}"
-    implementation "com.android.support:appcompat-v7:${mozconfig.substs.ANDROID_SUPPORT_LIBRARY_VERSION}"
-    implementation "com.android.support:cardview-v7:${mozconfig.substs.ANDROID_SUPPORT_LIBRARY_VERSION}"
-    implementation "com.android.support:recyclerview-v7:${mozconfig.substs.ANDROID_SUPPORT_LIBRARY_VERSION}"
-    implementation "com.android.support:design:${mozconfig.substs.ANDROID_SUPPORT_LIBRARY_VERSION}"
-    implementation "com.android.support:customtabs:${mozconfig.substs.ANDROID_SUPPORT_LIBRARY_VERSION}"
-    implementation "com.android.support:palette-v7:${mozconfig.substs.ANDROID_SUPPORT_LIBRARY_VERSION}"
+    implementation "com.android.support:support-v4:$support_library_version"
+    implementation "com.android.support:appcompat-v7:$support_library_version"
+    implementation "com.android.support:cardview-v7:$support_library_version"
+    implementation "com.android.support:recyclerview-v7:$support_library_version"
+    implementation "com.android.support:design:$support_library_version"
+    implementation "com.android.support:customtabs:$support_library_version"
+    implementation "com.android.support:palette-v7:$support_library_version"
 
     if (mozconfig.substs.MOZ_NATIVE_DEVICES) {
-        implementation "com.android.support:mediarouter-v7:${mozconfig.substs.ANDROID_SUPPORT_LIBRARY_VERSION}"
+        implementation "com.android.support:mediarouter-v7:$support_library_version"
         implementation "com.google.android.gms:play-services-basement:${mozconfig.substs.ANDROID_GOOGLE_PLAY_SERVICES_VERSION}"
         implementation "com.google.android.gms:play-services-base:${mozconfig.substs.ANDROID_GOOGLE_PLAY_SERVICES_VERSION}"
         implementation "com.google.android.gms:play-services-cast:${mozconfig.substs.ANDROID_GOOGLE_PLAY_SERVICES_VERSION}"
     }
 
     if (mozconfig.substs.MOZ_INSTALL_TRACKING) {
         implementation "com.google.android.gms:play-services-analytics:${mozconfig.substs.ANDROID_GOOGLE_PLAY_SERVICES_VERSION}"
         implementation "com.google.android.gms:play-services-basement:${mozconfig.substs.ANDROID_GOOGLE_PLAY_SERVICES_VERSION}"

--- a/mobile/android/geckoview/build.gradle
+++ b/mobile/android/geckoview/build.gradle
@@ -144,29 +144,29 @@ android {
 
             assets {
             }
         }
     }
 }
 
 dependencies {
-    implementation "com.android.support:support-v4:${mozconfig.substs.ANDROID_SUPPORT_LIBRARY_VERSION}"
-    implementation "com.android.support:palette-v7:${mozconfig.substs.ANDROID_SUPPORT_LIBRARY_VERSION}"
+    implementation "com.android.support:support-v4:$support_library_version"
+    implementation "com.android.support:palette-v7:$support_library_version"
 
     testImplementation "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version"
     testImplementation 'junit:junit:4.12'
     testImplementation 'org.robolectric:robolectric:3.5.1'
     testImplementation 'org.mockito:mockito-core:1.10.19'
 
     androidTestImplementation "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version"
     androidTestImplementation 'com.android.support.test:runner:0.5'
     androidTestImplementation 'com.android.support.test:rules:0.5'
     androidTestImplementation 'com.android.support.test.espresso:espresso-core:2.2.2'
-    androidTestImplementation "com.android.support:support-annotations:${mozconfig.substs.ANDROID_SUPPORT_LIBRARY_VERSION}"
+    androidTestImplementation "com.android.support:support-annotations:$support_library_version"
 }
 
 apply from: "${topsrcdir}/mobile/android/gradle/with_gecko_binaries.gradle"
 
 android.libraryVariants.all { variant ->
     // See the notes in mobile/android/app/build.gradle for details on including
     // Gecko binaries and the Omnijar.
     if ((variant.productFlavors*.name).contains('withGeckoBinaries')) {

--- a/mobile/android/geckoview_example/build.gradle
+++ b/mobile/android/geckoview_example/build.gradle
@@ -27,18 +27,18 @@ android {
 
     project.configureProductFlavors.delegate = it
     project.configureProductFlavors()
 }
 
 dependencies {
     testImplementation 'junit:junit:4.12'
 
-    implementation 'com.android.support:support-annotations:23.4.0'
+    implementation 'com.android.support:support-annotations:$support_library_version'
 
     androidTestImplementation 'com.android.support.test.espresso:espresso-core:2.2.2'
     androidTestImplementation 'com.android.support.test:runner:0.5'
     // Not defining this library again results in test-app assuming 23.1.1, and the following errors:
     // "Conflict with dependency 'com.android.support:support-annotations'. Resolved versions for app (23.4.0) and test app (23.1.1) differ."
-    androidTestImplementation 'com.android.support:support-annotations:23.4.0'
+    androidTestImplementation 'com.android.support:support-annotations:$support_library_version'
 
     implementation project(path: ':geckoview')
 }

--- a/mobile/android/moz.configure
+++ b/mobile/android/moz.configure
@@ -111,19 +111,16 @@ option(env='MOZ_ANDROID_MOZILLA_ONLINE',
 
 set_config('MOZ_ANDROID_MOZILLA_ONLINE',
            depends_if('MOZ_ANDROID_MOZILLA_ONLINE')(lambda _: True))
 
 imply_option('MOZ_SERVICES_HEALTHREPORT', True)
 imply_option('MOZ_ANDROID_HISTORY', True)
 imply_option('--enable-small-chunk-size', True)
 
-set_config('ANDROID_SUPPORT_LIBRARY_VERSION', '23.4.0')
-add_old_configure_assignment('ANDROID_SUPPORT_LIBRARY_VERSION', '23.4.0')
-
 @depends(target)
 def check_target(target):
     if target.os != 'Android':
         log.error('You must specify --target=arm-linux-androideabi (or some '
                   'other valid Android target) when building mobile/android.')
         die('See https://developer.mozilla.org/docs/Mozilla/Developer_guide/'
             'Build_Instructions/Simple_Firefox_for_Android_build '
             'for more information about the necessary options.')

--- a/mobile/android/thirdparty/build.gradle
+++ b/mobile/android/thirdparty/build.gradle
@@ -38,20 +38,20 @@ android {
                 // here is only the no-op library for mach-based builds.
                 exclude 'com/squareup/leakcanary/**'
             }
         }
     }
 }
 
 dependencies {
-    implementation "com.android.support:support-v4:${mozconfig.substs.ANDROID_SUPPORT_LIBRARY_VERSION}"
+    implementation "com.android.support:support-v4:$support_library_version"
     if (mozconfig.substs.MOZ_ANDROID_MMA) {
-        implementation "com.android.support:appcompat-v7:${mozconfig.substs.ANDROID_SUPPORT_LIBRARY_VERSION}"
-        implementation "com.android.support:support-annotations:${mozconfig.substs.ANDROID_GOOGLE_PLAY_SERVICES_VERSION}"
+        implementation "com.android.support:appcompat-v7:$support_library_version"
+        implementation "com.android.support:support-annotations:$support_library_version"
         implementation "com.google.android.gms:play-services-gcm:${mozconfig.substs.ANDROID_GOOGLE_PLAY_SERVICES_VERSION}"
     }
 }
 
 apply plugin: 'idea'
 
 idea {
     module {