--- a/gfx/src/nsDeviceContext.h
+++ b/gfx/src/nsDeviceContext.h
@@ -110,17 +110,17 @@ public:
      */
     static PRInt32 AppUnitsPerCSSPixel() { return 60; }
 
     /**
      * Gets the number of app units in one device pixel; this number
      * is usually a factor of AppUnitsPerCSSPixel(), although that is
      * not guaranteed.
      */
-    PRInt32 AppUnitsPerDevPixel() const { return mAppUnitsPerDevPixel; }
+    PRUint32 AppUnitsPerDevPixel() const { return mAppUnitsPerDevPixel; }
 
     /**
      * Convert device pixels which is used for gfx/thebes to nearest
      * (rounded) app units
      */
     nscoord GfxUnitsToAppUnits(gfxFloat aGfxUnits) const
     { return nscoord(NS_round(aGfxUnits * AppUnitsPerDevPixel())); }
 
@@ -306,17 +306,17 @@ protected:
     void ComputeFullAreaUsingScreen(nsRect *outRect);
     void FindScreen(nsIScreen **outScreen);
     void CalcPrintingSize();
     void UpdateScaledAppUnits();
 
     nscoord  mWidth;
     nscoord  mHeight;
     PRUint32 mDepth;
-    PRInt32  mAppUnitsPerDevPixel;
+    PRUint32  mAppUnitsPerDevPixel;
     PRInt32  mAppUnitsPerDevNotScaledPixel;
     PRInt32  mAppUnitsPerPhysicalInch;
     float    mPixelScale;
     float    mPrintingScale;
 
     nsFontCache*                   mFontCache;
     nsCOMPtr<nsIWidget>            mWidget;
     nsCOMPtr<nsIScreenManager>     mScreenManager;

--- a/gfx/src/nsFontMetrics.cpp
+++ b/gfx/src/nsFontMetrics.cpp
@@ -93,32 +93,32 @@ public:
                             Spacing* aSpacing) {
         NS_ERROR("This shouldn't be called because we never enable spacing");
     }
 };
 
 } // anon namespace
 
 nsFontMetrics::nsFontMetrics()
-    : mDeviceContext(nsnull), mP2A(-1), mTextRunRTL(PR_FALSE)
+    : mDeviceContext(nsnull), mP2A(0), mTextRunRTL(PR_FALSE)
 {
 }
 
 nsFontMetrics::~nsFontMetrics()
 {
     if (mDeviceContext)
         mDeviceContext->FontMetricsDeleted(this);
 }
 
 nsresult
 nsFontMetrics::Init(const nsFont& aFont, nsIAtom* aLanguage,
                     nsDeviceContext *aContext,
                     gfxUserFontSet *aUserFontSet)
 {
-    NS_ABORT_IF_FALSE(mP2A == -1, "already initialized");
+    NS_ABORT_IF_FALSE(mP2A == 0, "already initialized");
 
     mFont = aFont;
     mLanguage = aLanguage;
     mDeviceContext = aContext;
     mP2A = mDeviceContext->AppUnitsPerDevPixel();
 
     gfxFontStyle style(aFont.style,
                        aFont.weight,

--- a/gfx/src/nsFontMetrics.h
+++ b/gfx/src/nsFontMetrics.h
@@ -222,22 +222,22 @@ public:
                                          nsRenderingContext *aContext);
 
     void SetTextRunRTL(PRBool aIsRTL) { mTextRunRTL = aIsRTL; }
     PRBool GetTextRunRTL() { return mTextRunRTL; }
 
     gfxFontGroup* GetThebesFontGroup() { return mFontGroup; }
     gfxUserFontSet* GetUserFontSet() { return mFontGroup->GetUserFontSet(); }
 
-    PRInt32 AppUnitsPerDevPixel() { return mP2A; }
+    PRUint32 AppUnitsPerDevPixel() { return mP2A; }
 
 protected:
     const gfxFont::Metrics& GetMetrics() const;
 
     nsFont mFont;
     nsRefPtr<gfxFontGroup> mFontGroup;
     nsCOMPtr<nsIAtom> mLanguage;
     nsDeviceContext *mDeviceContext;
-    PRInt32 mP2A;
+    PRUint32 mP2A;
     PRPackedBool mTextRunRTL;
 };
 
 #endif /* NSFONTMETRICS__H__ */

--- a/gfx/src/nsRenderingContext.h
+++ b/gfx/src/nsRenderingContext.h
@@ -65,17 +65,17 @@ public:
     NS_INLINE_DECL_REFCOUNTING(nsRenderingContext)
 
     void Init(nsDeviceContext* aContext, gfxASurface* aThebesSurface);
     void Init(nsDeviceContext* aContext, gfxContext* aThebesContext);
 
     // These accessors will never return null.
     gfxContext *ThebesContext() { return mThebes; }
     nsDeviceContext *DeviceContext() { return mDeviceContext; }
-    PRInt32 AppUnitsPerDevPixel() { return mP2A; }
+    PRUint32 AppUnitsPerDevPixel() { return mP2A; }
 
     // Graphics state
 
     void PushState(void);
     void PopState(void);
     void IntersectClip(const nsRect& aRect);
     void SetClip(const nsIntRegion& aRegion);
     void SetLineStyle(nsLineStyle aLineStyle);

--- a/layout/base/nsPresContext.h
+++ b/layout/base/nsPresContext.h
@@ -587,17 +587,17 @@ public:
   float GetFullZoom() { return mFullZoom; }
   void SetFullZoom(float aZoom);
 
   nscoord GetAutoQualityMinFontSize() {
     return DevPixelsToAppUnits(mAutoQualityMinFontSizePixelsPref);
   }
   
   static PRInt32 AppUnitsPerCSSPixel() { return nsDeviceContext::AppUnitsPerCSSPixel(); }
-  PRInt32 AppUnitsPerDevPixel() const  { return mDeviceContext->AppUnitsPerDevPixel(); }
+  PRUint32 AppUnitsPerDevPixel() const  { return mDeviceContext->AppUnitsPerDevPixel(); }
   static PRInt32 AppUnitsPerCSSInch() { return nsDeviceContext::AppUnitsPerCSSInch(); }
 
   static nscoord CSSPixelsToAppUnits(PRInt32 aPixels)
   { return NSIntPixelsToAppUnits(aPixels,
                                  nsDeviceContext::AppUnitsPerCSSPixel()); }
 
   static nscoord CSSPixelsToAppUnits(float aPixels)
   { return NSFloatPixelsToAppUnits(aPixels,

--- a/view/src/nsViewManager.h
+++ b/view/src/nsViewManager.h
@@ -248,17 +248,17 @@ public: // NOT in nsIViewManager, so pri
   nsEventStatus HandleEvent(nsView* aView, nsGUIEvent* aEvent);
 
   PRBool IsRefreshEnabled() { return RootViewManager()->mUpdateBatchCnt == 0; }
 
   // Call this when you need to let the viewmanager know that it now has
   // pending updates.
   void PostPendingUpdate() { RootViewManager()->mHasPendingUpdates = PR_TRUE; }
 
-  PRInt32 AppUnitsPerDevPixel() const
+  PRUint32 AppUnitsPerDevPixel() const
   {
     return mContext->AppUnitsPerDevPixel();
   }
 
 private:
   nsRefPtr<nsDeviceContext> mContext;
   nsIViewObserver   *mObserver;
 

--- a/xpfe/appshell/src/nsXULWindow.cpp
+++ b/xpfe/appshell/src/nsXULWindow.cpp
@@ -2078,17 +2078,17 @@ NS_IMETHODIMP nsXULWindow::SetXULBrowser
   mXULBrowserWindow = aXULBrowserWindow;
   return NS_OK;
 }
 
 //*****************************************************************************
 // nsXULWindow: Accessors
 //*****************************************************************************
 
-PRInt32 nsXULWindow::AppUnitsPerDevPixel()
+PRUint32 nsXULWindow::AppUnitsPerDevPixel()
 {
   if (mWindow && mWindow->GetDeviceContext()) {
     mAppPerDev = mWindow->GetDeviceContext()->AppUnitsPerDevPixel();
   } else {
     NS_ERROR("nsXULWindow::AppUnitsPerDevPixel called with no window "
              "or no dev context");
   }
   return mAppPerDev;

--- a/xpfe/appshell/src/nsXULWindow.h
+++ b/xpfe/appshell/src/nsXULWindow.h
@@ -142,17 +142,17 @@ protected:
    void       EnableParent(PRBool aEnable);
    PRBool     ConstrainToZLevel(PRBool aImmediate, nsWindowZ *aPlacement,
                                 nsIWidget *aReqBelow, nsIWidget **aActualBelow);
    void       PlaceWindowLayersBehind(PRUint32 aLowLevel, PRUint32 aHighLevel,
                                       nsIXULWindow *aBehind);
    void       SetContentScrollbarVisibility(PRBool aVisible);
    PRBool     GetContentScrollbarVisibility();
    void       PersistentAttributesDirty(PRUint32 aDirtyFlags);
-   PRInt32    AppUnitsPerDevPixel();
+   PRUint32   AppUnitsPerDevPixel();
 
    nsChromeTreeOwner*      mChromeTreeOwner;
    nsContentTreeOwner*     mContentTreeOwner;
    nsContentTreeOwner*     mPrimaryContentTreeOwner;
    nsCOMPtr<nsIWidget>     mWindow;
    nsCOMPtr<nsIDocShell>   mDocShell;
    nsCOMPtr<nsIDOMWindow>  mDOMWindow;
    nsCOMPtr<nsIWeakReference> mParentWindow;