diff --git a/gfx/thebes/gfxPrefs.h b/gfx/thebes/gfxPrefs.h
index ef77c05f04cf..e0537b35e0a7 100644
--- a/gfx/thebes/gfxPrefs.h
+++ b/gfx/thebes/gfxPrefs.h
@@ -507,6 +507,7 @@ private:
   DECL_GFX_PREF(Once, "gfx.vsync.compositor.unobserve-count",  CompositorUnobserveCount, int32_t, 10);
 
   DECL_GFX_PREF(Once, "gfx.webrender.all",                     WebRenderAll, bool, false);
+  DECL_GFX_PREF(Once, "gfx.webrender.async-scene-build",       WebRenderAsyncSceneBuild, bool, false);
   DECL_GFX_PREF(Once, "gfx.webrender.enabled",                 WebRenderEnabledDoNotUseDirectly, bool, false);
   DECL_OVERRIDE_PREF(Live, "gfx.webrender.blob-images",        WebRenderBlobImages, gfxPrefs::WebRenderAll());
   DECL_GFX_PREF(Live, "gfx.webrender.blob.invalidation",       WebRenderBlobInvalidation, bool, false);
diff --git a/gfx/webrender_bindings/WebRenderAPI.cpp b/gfx/webrender_bindings/WebRenderAPI.cpp
index ac2fbd2d5856..63f9730a41b5 100644
--- a/gfx/webrender_bindings/WebRenderAPI.cpp
+++ b/gfx/webrender_bindings/WebRenderAPI.cpp
@@ -5,7 +5,9 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "WebRenderAPI.h"
+
 #include "DisplayItemClipChain.h"
+#include "gfxPrefs.h"
 #include "LayersLogging.h"
 #include "mozilla/webrender/RendererOGL.h"
 #include "mozilla/gfx/gfxVars.h"
@@ -134,8 +136,15 @@ private:
 
 TransactionBuilder::TransactionBuilder()
 {
-  mTxn = wr_transaction_new();
-  mResourceUpdates = wr_resource_updates_new();
+  // We need the if statement to avoid miscompilation on windows, see
+  // bug 1449982 comment 22.
+  if (gfxPrefs::WebRenderAsyncSceneBuild()) {
+    mTxn = wr_transaction_new(true);
+    mResourceUpdates = wr_resource_updates_new();
+  } else {
+    mResourceUpdates = wr_resource_updates_new();
+    mTxn = wr_transaction_new(false);
+  }
 }
 
 TransactionBuilder::~TransactionBuilder()
diff --git a/gfx/webrender_bindings/src/bindings.rs b/gfx/webrender_bindings/src/bindings.rs
index adc63e3847d1..5f921063bf3f 100644
--- a/gfx/webrender_bindings/src/bindings.rs
+++ b/gfx/webrender_bindings/src/bindings.rs
@@ -863,8 +863,17 @@ pub unsafe extern "C" fn wr_api_shut_down(dh: &mut DocumentHandle) {
 }
 
 #[no_mangle]
-pub extern "C" fn wr_transaction_new() -> *mut Transaction {
-    Box::into_raw(Box::new(Transaction::new()))
+pub extern "C" fn wr_transaction_new(do_async: bool) -> *mut Transaction {
+    let mut transaction = Transaction::new();
+    // Ensure that we either use async scene building or not based on the
+    // gecko pref, regardless of what the default is. We can remove this once
+    // the scene builder thread is enabled everywhere and working well.
+    if do_async {
+        transaction.use_scene_builder_thread();
+    } else {
+        transaction.skip_scene_builder();
+    }
+    Box::into_raw(Box::new(transaction))
 }
 
 /// cbindgen:postfix=WR_DESTRUCTOR_SAFE_FUNC
diff --git a/gfx/webrender_bindings/webrender_ffi_generated.h b/gfx/webrender_bindings/webrender_ffi_generated.h
index 03bd5387c0e4..75da8e85c66c 100644
--- a/gfx/webrender_bindings/webrender_ffi_generated.h
+++ b/gfx/webrender_bindings/webrender_ffi_generated.h
@@ -1580,7 +1580,7 @@ bool wr_transaction_is_empty(const Transaction *aTxn)
 WR_FUNC;
 
 WR_INLINE
-Transaction *wr_transaction_new()
+Transaction *wr_transaction_new(bool aDoAsync)
 WR_FUNC;
 
 WR_INLINE