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diff --git a/gfx/2d/ScaleFactors2D.h b/gfx/2d/ScaleFactors2D.h
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+/* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef MOZILLA_GFX_SCALEFACTORS2D_H_
+#define MOZILLA_GFX_SCALEFACTORS2D_H_
+
+#include <ostream>
+
+#include "mozilla/Attributes.h"
+#include "mozilla/FloatingPoint.h"
+#include "mozilla/gfx/ScaleFactor.h"
+
+#include "gfxPoint.h"
+
+namespace mozilla {
+namespace gfx {
+
+/*
+ * This class is like ScaleFactor, but allows different scales on the x and
+ * y axes.
+ */
+template<class src, class dst>
+struct ScaleFactors2D {
+  float xScale;
+  float yScale;
+
+  constexpr ScaleFactors2D() : xScale(1.0), yScale(1.0) {}
+  constexpr ScaleFactors2D(const ScaleFactors2D<src, dst>& aCopy)
+    : xScale(aCopy.xScale), yScale(aCopy.yScale) {}
+  constexpr ScaleFactors2D(float aXScale, float aYScale)
+    : xScale(aXScale), yScale(aYScale) {}
+  // Layout code often uses gfxSize to represent a pair of x/y scales.
+  explicit constexpr ScaleFactors2D(const gfxSize& aSize)
+    : xScale(aSize.width), yScale(aSize.height) {}
+
+  // "Upgrade" from a ScaleFactor.
+  // This is deliberately 'explicit' so that the treatment of a single scale
+  // number as both the x- and y-scale in a context where they are allowed to
+  // be different, is more visible.
+  explicit constexpr ScaleFactors2D(const ScaleFactor<src, dst>& aScale)
+    : xScale(aScale.scale), yScale(aScale.scale) {}
+
+  bool AreScalesSame() const {
+    return FuzzyEqualsMultiplicative(xScale, yScale);
+  }
+
+  // Convert to a ScaleFactor. Asserts that the scales are, in fact, equal.
+  ScaleFactor<src, dst> ToScaleFactor() const {
+    MOZ_ASSERT(AreScalesSame());
+    return ScaleFactor<src, dst>(xScale);
+  }
+
+  bool operator==(const ScaleFactors2D<src, dst>& aOther) const {
+    return xScale == aOther.xScale && yScale == aOther.yScale;
+  }
+
+  bool operator!=(const ScaleFactors2D<src, dst>& aOther) const {
+    return !(*this == aOther);
+  }
+
+  friend std::ostream& operator<<(std::ostream& aStream,
+                                  const ScaleFactors2D<src, dst>& aScale) {
+    if (aScale.AreScalesSame()) {
+      return aStream << aScale.xScale;
+    } else {
+      return aStream << '(' << aScale.xScale << ',' << aScale.yScale << ')';
+    }
+  }
+
+  template<class other>
+  ScaleFactors2D<other, dst> operator/(const ScaleFactors2D<src, other>& aOther) const {
+    return ScaleFactors2D<other, dst>(xScale / aOther.xScale, yScale / aOther.yScale);
+  }
+
+  template<class other>
+  ScaleFactors2D<src, other> operator/(const ScaleFactors2D<other, dst>& aOther) const {
+    return ScaleFactors2D<src, other>(xScale / aOther.xScale, yScale / aOther.yScale);
+  }
+
+  template<class other>
+  ScaleFactors2D<src, other> operator*(const ScaleFactors2D<dst, other>& aOther) const {
+    return ScaleFactors2D<src, other>(xScale * aOther.xScale, yScale * aOther.yScale);
+  }
+
+  template<class other>
+  ScaleFactors2D<other, dst> operator*(const ScaleFactors2D<other, src>& aOther) const {
+    return ScaleFactors2D<other, dst>(xScale * aOther.xScale, yScale * aOther.yScale);
+  }
+
+  template<class other>
+  ScaleFactors2D<src, other> operator*(const ScaleFactor<dst, other>& aOther) const {
+    return *this * ScaleFactors2D<dst, other>(aOther);
+  }
+
+  template<class other>
+  ScaleFactors2D<other, dst> operator*(const ScaleFactor<other, src>& aOther) const {
+    return *this * ScaleFactors2D<other, src>(aOther);
+  }
+
+  template<class other>
+  ScaleFactors2D<src, other> operator/(const ScaleFactor<other, dst>& aOther) const {
+    return *this / ScaleFactors2D<other, dst>(aOther);
+  }
+
+  template<class other>
+  ScaleFactors2D<other, dst> operator/(const ScaleFactor<src, other>& aOther) const {
+    return *this / ScaleFactors2D<src, other>(aOther);
+  }
+
+  template<class other>
+  friend ScaleFactors2D<other, dst> operator*(const ScaleFactor<other, src>& aA,
+                                              const ScaleFactors2D<src, dst>& aB) {
+    return ScaleFactors2D<other, src>(aA) * aB;
+  }
+
+  template<class other>
+  friend ScaleFactors2D<other, src> operator/(const ScaleFactor<other, dst>& aA,
+                                              const ScaleFactors2D<src, dst>& aB) {
+    return ScaleFactors2D<other, src>(aA) / aB;
+  }
+
+  // Divide two scales of the same units, yielding a scale with no units,
+  // represented as a gfxSize. This can mean e.g. the cahnge in a particular
+  // scale from one frame to the next.
+  gfxSize operator/(const ScaleFactors2D& aOther) const {
+    return gfxSize(xScale / aOther.xScale, yScale / aOther.yScale);
+  }
+};
+
+} // namespace gfx
+} // namespace mozilla
+
+#endif /* MOZILLA_GFX_SCALEFACTORS2D_H_ */