--- a/modules/libpr0n/src/imgContainer.cpp
+++ b/modules/libpr0n/src/imgContainer.cpp
@@ -134,34 +134,34 @@ DiscardingEnabled()
 }
 
 NS_IMPL_ISUPPORTS4(imgContainer, imgIContainer, nsITimerCallback, nsIProperties,
                    nsISupportsWeakReference)
 
 //******************************************************************************
 imgContainer::imgContainer() :
   mSize(0,0),
-  mHasSize(PR_FALSE),
   mAnim(nsnull),
   mAnimationMode(kNormalAnimMode),
   mLoopCount(-1),
   mObserver(nsnull),
+  mLockCount(0),
+  mDiscardTimer(nsnull),
+  mDecoder(nsnull),
+  mWorker(nsnull),
+  mBytesDecoded(0),
+  mDecoderFlags(imgIDecoder::DECODER_FLAG_NONE),
+  mHasSize(PR_FALSE),
   mDecodeOnDraw(PR_FALSE),
   mMultipart(PR_FALSE),
   mInitialized(PR_FALSE),
   mDiscardable(PR_FALSE),
-  mLockCount(0),
-  mDiscardTimer(nsnull),
   mHasSourceData(PR_FALSE),
   mDecoded(PR_FALSE),
   mHasBeenDecoded(PR_FALSE),
-  mDecoder(nsnull),
-  mWorker(nsnull),
-  mBytesDecoded(0),
-  mDecoderFlags(imgIDecoder::DECODER_FLAG_NONE),
   mWorkerPending(PR_FALSE),
   mInDecoder(PR_FALSE),
   mError(PR_FALSE)
 {
   // Statistics
   num_containers++;
 }
 

--- a/modules/libpr0n/src/imgContainer.h
+++ b/modules/libpr0n/src/imgContainer.h
@@ -159,21 +159,16 @@ private:
   {
     //! Area of the first frame that needs to be redrawn on subsequent loops.
     nsIntRect                  firstFrameRefreshArea;
     // Note this doesn't hold a proper value until frame 2 finished decoding.
     PRUint32                   currentDecodingFrameIndex; // 0 to numFrames-1
     PRUint32                   currentAnimationFrameIndex; // 0 to numFrames-1
     //! Track the last composited frame for Optimizations (See DoComposite code)
     PRInt32                    lastCompositedFrameIndex;
-    //! Whether we can assume there will be no more frames
-    //! (and thus loop the animation)
-    PRBool                     doneDecoding;
-    //! Are we currently animating the image?
-    PRBool                     animating;
     /** For managing blending of frames
      *
      * Some animations will use the compositingFrame to composite images
      * and just hand this back to the caller when it is time to draw the frame.
      * NOTE: When clearing compositingFrame, remember to set
      *       lastCompositedFrameIndex to -1.  Code assume that if
      *       lastCompositedFrameIndex >= 0 then compositingFrame exists.
      */
@@ -182,17 +177,22 @@ private:
      *
      * The Previous Frame (all frames composited up to the current) needs to be
      * stored in cases where the image specifies it wants the last frame back
      * when it's done with the current frame.
      */
     nsAutoPtr<imgFrame>        compositingPrevFrame;
     //! Timer to animate multiframed images
     nsCOMPtr<nsITimer>         timer;
-    
+    //! Whether we can assume there will be no more frames
+    //! (and thus loop the animation)
+    PRPackedBool               doneDecoding;
+    //! Are we currently animating the image?
+    PRPackedBool               animating;
+
     Anim() :
       firstFrameRefreshArea(),
       currentDecodingFrameIndex(0),
       currentAnimationFrameIndex(0),
       lastCompositedFrameIndex(-1),
       doneDecoding(PR_FALSE),
       animating(PR_FALSE)
     {
@@ -288,17 +288,16 @@ private:
   nsresult InternalAddFrame(PRUint32 framenum, PRInt32 aX, PRInt32 aY, PRInt32 aWidth, PRInt32 aHeight,
                             gfxASurface::gfxImageFormat aFormat, PRUint8 aPaletteDepth,
                             PRUint8 **imageData, PRUint32 *imageLength,
                             PRUint32 **paletteData, PRUint32 *paletteLength);
 
 private: // data
 
   nsIntSize                  mSize;
-  PRBool                     mHasSize;
   
   //! All the frames of the image
   // IMPORTANT: if you use mFrames in a method, call EnsureImageIsDecoded() first 
   // to ensure that the frames actually exist (they may have been discarded to save
   // memory, or we may be decoding on draw).
   nsTArray<imgFrame *>       mFrames;
   
   nsCOMPtr<nsIProperties>    mProperties;
@@ -312,51 +311,49 @@ private: // data
   PRUint16                   mAnimationMode;
   
   //! # loops remaining before animation stops (-1 no stop)
   PRInt32                    mLoopCount;
   
   //! imgIDecoderObserver
   nsWeakPtr                  mObserver;
 
-  // Decoding on draw?
-  PRBool                     mDecodeOnDraw;
-
-  // Multipart?
-  PRBool                     mMultipart;
-
-  // Have we been initalized?
-  PRBool                     mInitialized;
-
   // Discard members
-  PRBool                     mDiscardable;
   PRUint32                   mLockCount;
   nsCOMPtr<nsITimer>         mDiscardTimer;
 
   // Source data members
   nsTArray<char>             mSourceData;
-  PRBool                     mHasSourceData;
   nsCString                  mSourceDataMimeType;
 
-  // Do we have the frames in decoded form?
-  PRBool                     mDecoded;
-  PRBool                     mHasBeenDecoded;
-
   friend class imgDecodeWorker;
 
   // Decoder and friends
   nsCOMPtr<imgIDecoder>          mDecoder;
   nsRefPtr<imgDecodeWorker>      mWorker;
   PRUint32                       mBytesDecoded;
   PRUint32                       mDecoderFlags;
-  PRBool                         mWorkerPending;
-  PRBool                         mInDecoder;
+
+  // Boolean flags (clustered together to conserve space):
+  PRPackedBool               mHasSize:1;       // Has SetSize() been called?
+  PRPackedBool               mDecodeOnDraw:1;  // Decoding on draw?
+  PRPackedBool               mMultipart:1;     // Multipart?
+  PRPackedBool               mInitialized:1;   // Have we been initalized?
+  PRPackedBool               mDiscardable:1;   // Is container discardable?
+  PRPackedBool               mHasSourceData:1; // Do we have source data?
 
-  // Error handling
-  PRBool                         mError;
+  // Do we have the frames in decoded form?
+  PRPackedBool               mDecoded:1;
+  PRPackedBool               mHasBeenDecoded:1;
+
+  // Helpers for decoder
+  PRPackedBool               mWorkerPending:1;
+  PRPackedBool               mInDecoder:1;
+
+  PRPackedBool               mError:1;  // Error handling
 
   // Discard code
   nsresult ResetDiscardTimer();
   static void sDiscardTimerCallback(nsITimer *aTimer, void *aClosure);
 
   // Decoding
   nsresult WantDecodedFrames();
   nsresult SyncDecode();