Bug 663776. Part 1: When determining whether the scale factors hav changed, we need to use GetBaseTransform for the old scale factors, because that's what stores the old transform that we computed scale factors from. r=mattwoodrow

layout/base/FrameLayerBuilder.cpp

@@ -2783,10 +2783,11 @@ ChooseScaleAndSetTransform(FrameLayerBuilder* aLayerBuilder,
       // or it was previously unscaled.
       bool clamp = true;
       gfxMatrix oldFrameTransform2d;
-      if (aLayer->GetTransform().Is2D(&oldFrameTransform2d)) {
+      if (aLayer->GetBaseTransform().Is2D(&oldFrameTransform2d)) {
         gfxSize oldScale = oldFrameTransform2d.ScaleFactors(true);
-        if (oldScale == scale || oldScale == gfxSize(1.0, 1.0))
+        if (oldScale == scale || oldScale == gfxSize(1.0, 1.0)) {
           clamp = false;
+        }
       }
       if (clamp) {
         scale.width = gfxUtils::ClampToScaleFactor(scale.width);