--- a/gfx/thebes/gfxPlatform.cpp
+++ b/gfx/thebes/gfxPlatform.cpp
@@ -2296,22 +2296,23 @@ gfxPlatform::InitCompositorAccelerationP
   }
 }
 
 void
 gfxPlatform::InitWebRenderConfig()
 {
   FeatureState& featureWebRender = gfxConfig::GetFeature(Feature::WEBRENDER);
 
-  featureWebRender.EnableByDefault();
-
-  if (!Preferences::GetBool("gfx.webrender.enabled", false)) {
-    featureWebRender.UserDisable(
-      "User disabled WebRender",
-      NS_LITERAL_CSTRING("FEATURE_FAILURE_WEBRENDER_DISABLED"));
+  featureWebRender.DisableByDefault(
+      FeatureStatus::OptIn,
+      "WebRender is an opt-in feature",
+      NS_LITERAL_CSTRING("FEATURE_FAILURE_DEFAULT_OFF"));
+
+  if (Preferences::GetBool("gfx.webrender.enabled", false)) {
+    featureWebRender.UserEnable("Enabled by pref");
   }
 
   // WebRender relies on the GPU process when on Windows
 #ifdef XP_WIN
   if (!gfxConfig::IsEnabled(Feature::GPU_PROCESS)) {
     featureWebRender.ForceDisable(
       FeatureStatus::Unavailable,
       "GPU Process is disabled",

--- a/modules/libpref/init/all.js
+++ b/modules/libpref/init/all.js
@@ -813,17 +813,21 @@ pref("gfx.work-around-driver-bugs", true
 pref("gfx.draw-color-bars", false);
 
 pref("gfx.logging.painted-pixel-count.enabled", false);
 pref("gfx.logging.texture-usage.enabled", false);
 pref("gfx.logging.peak-texture-usage.enabled", false);
 
 pref("gfx.ycbcr.accurate-conversion", false);
 
+#ifdef MOZ_ENABLE_WEBRENDER
 pref("gfx.webrender.enabled", true);
+#else
+pref("gfx.webrender.enabled", false);
+#endif
 
 pref("accessibility.browsewithcaret", false);
 pref("accessibility.warn_on_browsewithcaret", true);
 
 pref("accessibility.browsewithcaret_shortcut.enabled", true);
 
 #ifndef XP_MACOSX
 // Tab focus model bit field:
@@ -5640,13 +5644,13 @@ pref("dom.moduleScripts.enabled", false)
 pref("dom.timeout.max_consecutive_callbacks", 5);
 
 #ifdef FUZZING
 pref("fuzzing.enabled", false);
 #endif
 
 // Set advanced layers preferences here.
 pref("layers.advanced.border-layers", false);
-#ifdef MOZ_BUILD_WEBRENDER
+#ifdef MOZ_ENABLE_WEBRENDER
 pref("layers.advanced.caret-layers", true);
 #else
 pref("layers.advanced.caret-layers", false);
 #endif

--- a/modules/libpref/moz.build
+++ b/modules/libpref/moz.build
@@ -40,12 +40,14 @@ SOURCES += [
 ]
 
 include('/ipc/chromium/chromium-config.mozbuild')
 
 FINAL_LIBRARY = 'xul'
 
 DEFINES['OS_ARCH'] = CONFIG['OS_ARCH']
 DEFINES['MOZ_WIDGET_TOOLKIT'] = CONFIG['MOZ_WIDGET_TOOLKIT']
+if CONFIG['MOZ_ENABLE_WEBRENDER']:
+    DEFINES['MOZ_ENABLE_WEBRENDER'] = True
 
 FINAL_TARGET_PP_FILES += [
     'greprefs.js',
 ]

--- a/toolkit/moz.configure
+++ b/toolkit/moz.configure
@@ -688,22 +688,47 @@ option('--with-servo', env='SERVO_TARGET
 
 @depends_if('--with-servo')
 def servo_target_dir(value):
     return value[0]
 
 set_config('SERVO_TARGET_DIR', servo_target_dir)
 
 # WebRender integration
-option('--enable-webrender', help='Include WebRender')
+option('--enable-webrender', nargs='?', choices=('build',),
+       help='Include WebRender in the build and/or enable it at runtime')
+
+@depends('--enable-webrender', milestone, target)
+def webrender(value, milestone, target):
+    build_webrender = None
+    enable_webrender = None
 
-set_config('MOZ_BUILD_WEBRENDER',
-           depends_if('--enable-webrender')(lambda _: True))
-set_define('MOZ_BUILD_WEBRENDER',
-           depends_if('--enable-webrender')(lambda _: True))
+    if target.os == 'Android':
+        # we can't yet build WebRender on Android, see bug 1323612.
+        pass
+    elif value.origin == 'default':
+        # if nothing is specified, default to just building on Nightly
+        build_webrender = milestone.is_nightly
+    elif value == 'build':
+        # if explicitly set to 'build', then we build but don't enable
+        build_webrender = True
+    elif bool(value):
+        # if set to true, then build and enable
+        build_webrender = True
+        enable_webrender = True
+
+    # in all other cases, don't build it or enable it (defaults are fine)
+    return namespace(
+        build = build_webrender,
+        enable = enable_webrender,
+    )
+
+set_config('MOZ_BUILD_WEBRENDER', delayed_getattr(webrender, 'build'))
+set_define('MOZ_BUILD_WEBRENDER', delayed_getattr(webrender, 'build'))
+set_config('MOZ_ENABLE_WEBRENDER', delayed_getattr(webrender, 'enable'))
 
 # Printing
 # ==============================================================
 @depends(target)
 def ios_disable_printing(target):
     if target.os == 'iOS':
         return False