diff --git a/gfx/2d/DrawTargetD2D1.cpp b/gfx/2d/DrawTargetD2D1.cpp
index 6c8175e9983a..0df50ac8cea4 100644
--- a/gfx/2d/DrawTargetD2D1.cpp
+++ b/gfx/2d/DrawTargetD2D1.cpp
@@ -15,6 +15,7 @@
 #include "FilterNodeD2D1.h"
 #include "ExtendInputEffectD2D1.h"
 #include "Tools.h"
+#include "nsAppRunner.h"
 
 using namespace std;
 
@@ -119,7 +120,10 @@ DrawTargetD2D1::EnsureLuminanceEffect()
 already_AddRefed<SourceSurface>
 DrawTargetD2D1::IntoLuminanceSource(LuminanceType aLuminanceType, float aOpacity)
 {
-  if (aLuminanceType != LuminanceType::LUMINANCE) {
+  if ((aLuminanceType != LuminanceType::LUMINANCE) ||
+      // See bug 1372577, some race condition where we get invalid
+      // results with D2D in the parent process. Fallback in that case.
+      XRE_IsParentProcess()) {
     return DrawTarget::IntoLuminanceSource(aLuminanceType, aOpacity);
   }
 
diff --git a/layout/reftests/w3c-css/submitted/masking/reftest.list b/layout/reftests/w3c-css/submitted/masking/reftest.list
index 41118dd9dee1..b0b470362057 100644
--- a/layout/reftests/w3c-css/submitted/masking/reftest.list
+++ b/layout/reftests/w3c-css/submitted/masking/reftest.list
@@ -27,8 +27,9 @@ fuzzy-if(skiaContent||winWidget,1,20000) == mask-image-2.html mask-image-2-ref.h
 fuzzy-if(skiaContent||winWidget,1,43) == mask-image-3c.html mask-image-3-ref.html
 fuzzy-if(skiaContent||winWidget,1,43) == mask-image-3d.html mask-image-3-ref.html
 == mask-image-3e.html mask-image-3-ref.html
-fuzzy-if(skiaContent||winWidget,50,85) fuzzy-if(webrender,1,126) fuzzy-if(d2d,255,1) == mask-image-3f.html mask-image-3-ref.html
-fuzzy-if(skiaContent||winWidget,50,85) fuzzy-if(webrender,1,126) fuzzy-if(d2d,255,1) == mask-image-3g.html mask-image-3-ref.html
+# Due to SVG luminance, see bug 1372577, parent process doesn't use d2d for luminance.
+fuzzy-if(skiaContent||winWidget,50,85) fuzzy-if(webrender,1,126) fuzzy-if(d2d,255,1) fuzzy-if(winWidget&&!browserIsRemote,50,85) == mask-image-3f.html mask-image-3-ref.html
+fuzzy-if(skiaContent||winWidget,50,85) fuzzy-if(webrender,1,126) fuzzy-if(d2d,255,1) fuzzy-if(winWidget&&!browserIsRemote,50,85) == mask-image-3g.html mask-image-3-ref.html
 pref(layout.css.clip-path-shapes.enabled,true) fuzzy-if(winWidget,1,3) fuzzy-if(skiaContent,2,12) == mask-image-3h.html mask-image-3-ref.html
 fuzzy-if(skiaContent,71,203) == mask-image-3i.html mask-image-3-ref.html
 == mask-image-4a.html blank.html