--- a/gfx/thebes/gfxDWriteFontList.cpp
+++ b/gfx/thebes/gfxDWriteFontList.cpp
@@ -45,16 +45,18 @@
 #include "nsIPrefService.h"
 #include "nsIPrefBranch2.h"
 #include "nsServiceManagerUtils.h"
 
 #include "gfxGDIFontList.h"
 
 #include "nsIWindowsRegKey.h"
 
+using namespace mozilla;
+
 #ifdef PR_LOGGING
 
 #define LOG_FONTLIST(args) PR_LOG(gfxPlatform::GetLog(eGfxLog_fontlist), \
                                PR_LOG_DEBUG, args)
 #define LOG_FONTLIST_ENABLED() PR_LOG_TEST( \
                                    gfxPlatform::GetLog(eGfxLog_fontlist), \
                                    PR_LOG_DEBUG)
 
@@ -428,16 +430,51 @@ gfxDWriteFontEntry::InitLogFont(IDWriteF
 
     BOOL isInSystemCollection;
     IDWriteGdiInterop *gdi = 
         gfxDWriteFontList::PlatformFontList()->GetGDIInterop();
     hr = gdi->ConvertFontToLOGFONT(aFont, aLogFont, &isInSystemCollection);
     return (FAILED(hr) ? PR_FALSE : PR_TRUE);
 }
 
+PRBool
+gfxDWriteFontEntry::IsCJKFont()
+{
+    if (mIsCJK != UNINITIALIZED_VALUE) {
+        return mIsCJK;
+    }
+
+    mIsCJK = PR_FALSE;
+
+    const PRUint32 kOS2Tag = TRUETYPE_TAG('O','S','/','2');
+    AutoFallibleTArray<PRUint8,128> buffer;
+    if (GetFontTable(kOS2Tag, buffer) != NS_OK) {
+        return mIsCJK;
+    }
+
+    // ulCodePageRange bit definitions for the CJK codepages,
+    // from http://www.microsoft.com/typography/otspec/os2.htm#cpr
+    const PRUint32 CJK_CODEPAGE_BITS =
+        (1 << 17) | // codepage 932 - JIS/Japan
+        (1 << 18) | // codepage 936 - Chinese (simplified)
+        (1 << 19) | // codepage 949 - Korean Wansung
+        (1 << 20) | // codepage 950 - Chinese (traditional)
+        (1 << 21);  // codepage 1361 - Korean Johab
+
+    if (buffer.Length() >= offsetof(OS2Table, sxHeight)) {
+        const OS2Table* os2 =
+            reinterpret_cast<const OS2Table*>(buffer.Elements());
+        if ((PRUint32(os2->codePageRange1) & CJK_CODEPAGE_BITS) != 0) {
+            mIsCJK = PR_TRUE;
+        }
+    }
+
+    return mIsCJK;
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // gfxDWriteFontList
 
 gfxDWriteFontList::gfxDWriteFontList()
     : mInitialized(PR_FALSE)
 {
     mFontSubstitutes.Init();
 }

--- a/gfx/thebes/gfxDWriteFontList.h
+++ b/gfx/thebes/gfxDWriteFontList.h
@@ -98,18 +98,19 @@ public:
     {
         mItalic = (aFont->GetStyle() == DWRITE_FONT_STYLE_ITALIC ||
                    aFont->GetStyle() == DWRITE_FONT_STYLE_OBLIQUE);
         mStretch = FontStretchFromDWriteStretch(aFont->GetStretch());
         PRUint16 weight = PR_ROUNDUP(aFont->GetWeight() - 50, 100);
 
         weight = NS_MAX<PRUint16>(100, weight);
         weight = NS_MIN<PRUint16>(900, weight);
+        mWeight = weight;
 
-        mWeight = weight;
+        mIsCJK = UNINITIALIZED_VALUE;
     }
 
     /**
      * Constructs a font entry using a font. But with custom font values.
      * This is used for creating correct font entries for @font-face with local
      * font source.
      *
      * \param aFaceName The name of the corresponding font face.
@@ -125,16 +126,17 @@ public:
                               PRBool aItalic)
       : gfxFontEntry(aFaceName), mFont(aFont), mFontFile(nsnull)
     {
         mWeight = aWeight;
         mStretch = aStretch;
         mItalic = aItalic;
         mIsUserFont = PR_TRUE;
         mIsLocalUserFont = PR_TRUE;
+        mIsCJK = UNINITIALIZED_VALUE;
     }
 
     /**
      * Constructs a font entry using a font file.
      *
      * \param aFaceName The name of the corresponding font face.
      * \param aFontFile DirectWrite fontfile object
      * \param aWeight Weight of the font
@@ -147,26 +149,30 @@ public:
                               PRInt16 aStretch,
                               PRBool aItalic)
       : gfxFontEntry(aFaceName), mFont(nsnull), mFontFile(aFontFile)
     {
         mWeight = aWeight;
         mStretch = aStretch;
         mItalic = aItalic;
         mIsUserFont = PR_TRUE;
+        mIsCJK = UNINITIALIZED_VALUE;
     }
 
     virtual ~gfxDWriteFontEntry();
 
     virtual PRBool IsSymbolFont();
 
     virtual nsresult GetFontTable(PRUint32 aTableTag,
                                   FallibleTArray<PRUint8>& aBuffer);
 
     nsresult ReadCMAP();
+
+    PRBool IsCJKFont();
+
 protected:
     friend class gfxDWriteFont;
     friend class gfxDWriteFontList;
 
     virtual gfxFont *CreateFontInstance(const gfxFontStyle *aFontStyle,
                                         PRBool aNeedsBold);
     
     nsresult CreateFontFace(
@@ -177,16 +183,18 @@ protected:
 
     /**
      * A fontentry only needs to have either of these. If it has both only
      * the IDWriteFont will be used.
      */
     nsRefPtr<IDWriteFont> mFont;
     nsRefPtr<IDWriteFontFile> mFontFile;
     DWRITE_FONT_FACE_TYPE mFaceType;
+
+    PRBool mIsCJK;
 };
 
 
 class gfxDWriteFontList : public gfxPlatformFontList {
 public:
     gfxDWriteFontList();
 
     static gfxDWriteFontList* PlatformFontList() {

--- a/gfx/thebes/gfxDWriteFonts.cpp
+++ b/gfx/thebes/gfxDWriteFonts.cpp
@@ -220,17 +220,19 @@ gfxDWriteFont::ComputeMetrics()
     if (mStyle.sizeAdjust != 0.0) {
         gfxFloat aspect = (gfxFloat)fontMetrics.xHeight /
                    fontMetrics.designUnitsPerEm;
         mAdjustedSize = mStyle.GetAdjustedSize(aspect);
     } else {
         mAdjustedSize = mStyle.size;
     }
 
-    if (HasBitmapStrikeForSize(NS_lround(mAdjustedSize))) {
+    gfxDWriteFontEntry *fe =
+        static_cast<gfxDWriteFontEntry*>(mFontEntry.get());
+    if (fe->IsCJKFont() && HasBitmapStrikeForSize(NS_lround(mAdjustedSize))) {
         mAdjustedSize = NS_lround(mAdjustedSize);
         mUseSubpixelPositions = PR_FALSE;
         // if we have bitmaps, we need to tell Cairo NOT to use subpixel AA,
         // to avoid the manual-subpixel codepath in cairo-d2d-surface.cpp
         // which fails to render bitmap glyphs (see bug 626299)
         if (mAntialiasOption == kAntialiasDefault && UsingClearType()) {
             mAntialiasOption = kAntialiasGrayscale;
         }