diff --git a/gfx/2d/BaseRect.h b/gfx/2d/BaseRect.h
index 85a1532910af..593e7468ce2b 100644
--- a/gfx/2d/BaseRect.h
+++ b/gfx/2d/BaseRect.h
@@ -106,7 +106,7 @@ struct BaseRect {
   // (including edges) of *this and aRect. If there are no points in that
   // intersection, returns an empty rectangle with x/y set to the std::max of the x/y
   // of *this and aRect.
-  Sub Intersect(const Sub& aRect) const
+  MOZ_WARN_UNUSED_RESULT Sub Intersect(const Sub& aRect) const
   {
     Sub result;
     result.x = std::max<T>(x, aRect.x);
@@ -134,7 +134,7 @@ struct BaseRect {
   // this and aRect2.
   // Thus, empty input rectangles are ignored.
   // If both rectangles are empty, returns this.
-  Sub Union(const Sub& aRect) const
+  MOZ_WARN_UNUSED_RESULT Sub Union(const Sub& aRect) const
   {
     if (IsEmpty()) {
       return aRect;
@@ -147,7 +147,7 @@ struct BaseRect {
   // Returns the smallest rectangle that contains both the points (including
   // edges) of both aRect1 and aRect2.
   // Thus, empty input rectangles are allowed to affect the result.
-  Sub UnionEdges(const Sub& aRect) const
+  MOZ_WARN_UNUSED_RESULT Sub UnionEdges(const Sub& aRect) const
   {
     Sub result;
     result.x = std::min(x, aRect.x);
@@ -525,7 +525,7 @@ struct BaseRect {
    * Clamp aPoint to this rectangle. It is allowed to end up on any
    * edge of the rectangle.
    */
-  Point ClampPoint(const Point& aPoint) const
+  MOZ_WARN_UNUSED_RESULT Point ClampPoint(const Point& aPoint) const
   {
     return Point(std::max(x, std::min(XMost(), aPoint.x)),
                  std::max(y, std::min(YMost(), aPoint.y)));
@@ -536,7 +536,7 @@ struct BaseRect {
    * this rect after it is forced inside the bounds of aRect. It will attempt to
    * retain the size but will shrink the dimensions that don't fit.
    */
-  Sub ForceInside(const Sub& aRect) const
+  MOZ_WARN_UNUSED_RESULT Sub ForceInside(const Sub& aRect) const
   {
     Sub rect(std::max(aRect.x, x),
              std::max(aRect.y, y),
diff --git a/gfx/src/nsRect.h b/gfx/src/nsRect.h
index 8cbe64add926..e02750ae1f99 100644
--- a/gfx/src/nsRect.h
+++ b/gfx/src/nsRect.h
@@ -59,7 +59,7 @@ struct NS_GFX nsRect :
   // overflowing nscoord values in the 'width' and 'height' fields by
   // clamping the width and height values to nscoord_MAX if necessary.
 
-  nsRect SaturatingUnion(const nsRect& aRect) const
+  MOZ_WARN_UNUSED_RESULT nsRect SaturatingUnion(const nsRect& aRect) const
   {
     if (IsEmpty()) {
       return aRect;
@@ -70,7 +70,7 @@ struct NS_GFX nsRect :
     }
   }
 
-  nsRect SaturatingUnionEdges(const nsRect& aRect) const
+  MOZ_WARN_UNUSED_RESULT nsRect SaturatingUnionEdges(const nsRect& aRect) const
   {
 #ifdef NS_COORD_IS_FLOAT
     return UnionEdges(aRect);
@@ -107,7 +107,7 @@ struct NS_GFX nsRect :
 
 #ifndef NS_COORD_IS_FLOAT
   // Make all nsRect Union methods be saturating.
-  nsRect UnionEdges(const nsRect& aRect) const
+  MOZ_WARN_UNUSED_RESULT nsRect UnionEdges(const nsRect& aRect) const
   {
     return SaturatingUnionEdges(aRect);
   }
@@ -115,7 +115,7 @@ struct NS_GFX nsRect :
   {
     *this = aRect1.UnionEdges(aRect2);
   }
-  nsRect Union(const nsRect& aRect) const
+  MOZ_WARN_UNUSED_RESULT nsRect Union(const nsRect& aRect) const
   {
     return SaturatingUnion(aRect);
   }
@@ -148,17 +148,28 @@ struct NS_GFX nsRect :
   MOZ_WARN_UNUSED_RESULT inline nsRect
     ScaleToOtherAppUnitsRoundIn(int32_t aFromAPP, int32_t aToAPP) const;
 
-  inline nsIntRect ScaleToNearestPixels(float aXScale, float aYScale,
-                                        nscoord aAppUnitsPerPixel) const;
-  inline nsIntRect ToNearestPixels(nscoord aAppUnitsPerPixel) const;
+  MOZ_WARN_UNUSED_RESULT inline nsIntRect
+  ScaleToNearestPixels(float aXScale, float aYScale,
+                       nscoord aAppUnitsPerPixel) const;
+
+  MOZ_WARN_UNUSED_RESULT inline nsIntRect
+  ToNearestPixels(nscoord aAppUnitsPerPixel) const;
+
   // Note: this can turn an empty rectangle into a non-empty rectangle
-  inline nsIntRect ScaleToOutsidePixels(float aXScale, float aYScale,
-                                        nscoord aAppUnitsPerPixel) const;
+  MOZ_WARN_UNUSED_RESULT inline nsIntRect
+  ScaleToOutsidePixels(float aXScale, float aYScale,
+                       nscoord aAppUnitsPerPixel) const;
+
   // Note: this can turn an empty rectangle into a non-empty rectangle
-  inline nsIntRect ToOutsidePixels(nscoord aAppUnitsPerPixel) const;
-  inline nsIntRect ScaleToInsidePixels(float aXScale, float aYScale,
-                                       nscoord aAppUnitsPerPixel) const;
-  inline nsIntRect ToInsidePixels(nscoord aAppUnitsPerPixel) const;
+  MOZ_WARN_UNUSED_RESULT inline nsIntRect
+  ToOutsidePixels(nscoord aAppUnitsPerPixel) const;
+
+  MOZ_WARN_UNUSED_RESULT inline nsIntRect
+  ScaleToInsidePixels(float aXScale, float aYScale,
+                      nscoord aAppUnitsPerPixel) const;
+
+  MOZ_WARN_UNUSED_RESULT inline nsIntRect
+  ToInsidePixels(nscoord aAppUnitsPerPixel) const;
 
   // This is here only to keep IPDL-generated code happy. DO NOT USE.
   bool operator==(const nsRect& aRect) const
@@ -186,7 +197,8 @@ struct NS_GFX nsIntRect :
   {
   }
 
-  inline nsRect ToAppUnits(nscoord aAppUnitsPerPixel) const;
+  MOZ_WARN_UNUSED_RESULT inline nsRect
+  ToAppUnits(nscoord aAppUnitsPerPixel) const;
 
   // Returns a special nsIntRect that's used in some places to signify
   // "all available space".