diff --git a/gfx/thebes/public/gfxCoreTextFonts.h b/gfx/thebes/public/gfxCoreTextFonts.h
index da8dde8b482b..30a9f43be391 100644
--- a/gfx/thebes/public/gfxCoreTextFonts.h
+++ b/gfx/thebes/public/gfxCoreTextFonts.h
@@ -109,7 +109,7 @@ public:
     // clean up static objects that may have been cached
     static void Shutdown();
 
-    static CTFontRef CreateCopyWithDisabledLigatures(CTFontRef aFont);
+    static CTFontRef CreateCTFontWithDisabledLigatures(ATSFontRef aFont, CGFloat aSize);
 
 protected:
     const gfxFontStyle *mFontStyle;
diff --git a/gfx/thebes/src/gfxCoreTextFonts.cpp b/gfx/thebes/src/gfxCoreTextFonts.cpp
index 98c293e97c59..5d31b8ea4f7d 100644
--- a/gfx/thebes/src/gfxCoreTextFonts.cpp
+++ b/gfx/thebes/src/gfxCoreTextFonts.cpp
@@ -77,6 +77,26 @@ static PRLogModuleInfo *gCoreTextTextRunLog = PR_NewLogModule("coreTextTextRun")
 CTFontDescriptorRef gfxCoreTextFont::sDefaultFeaturesDescriptor = NULL;
 CTFontDescriptorRef gfxCoreTextFont::sDisableLigaturesDescriptor = NULL;
 
+#ifdef DEBUG_jonathan
+static void dumpFontDescCallback(const void *key, const void *value, void *context)
+{
+    CFStringRef attribute = (CFStringRef)key;
+    CFTypeRef setting = (CFTypeRef)value;
+    fprintf(stderr, "attr: "); CFShow(attribute);
+    fprintf(stderr, "    = "); CFShow(setting);
+    fprintf(stderr, "\n");
+}
+
+static void
+dumpFontDescriptor(CTFontRef font)
+{
+    CTFontDescriptorRef desc = CTFontCopyFontDescriptor(font);
+    CFDictionaryRef dict = CTFontDescriptorCopyAttributes(desc);
+    CFRelease(desc);
+    CFDictionaryApplyFunction(dict, &dumpFontDescCallback, 0);
+    CFRelease(dict);
+}
+#endif
 
 gfxCoreTextFont::gfxCoreTextFont(MacOSFontEntry *aFontEntry,
                                  const gfxFontStyle *aFontStyle,
@@ -451,9 +471,9 @@ gfxCoreTextFont::CreateDefaultFeaturesDescriptor()
     CFRelease(attributesDict);
 }
 
-// Create a copy of a CTFontRef, with the Common Ligatures feature disabled [static]
+// Create a CTFontRef for an ATS font ref, with the Common Ligatures feature disabled [static]
 CTFontRef
-gfxCoreTextFont::CreateCopyWithDisabledLigatures(CTFontRef aFontRef)
+gfxCoreTextFont::CreateCTFontWithDisabledLigatures(ATSFontRef aFontRef, CGFloat aSize)
 {
     if (sDisableLigaturesDescriptor == NULL) {
         // initialize cached descriptor to turn off the Common Ligatures feature
@@ -499,16 +519,11 @@ gfxCoreTextFont::CreateCopyWithDisabledLigatures(CTFontRef aFontRef)
         CFRelease(featuresArray);
 
         sDisableLigaturesDescriptor =
-            CTFontDescriptorCreateWithAttributes(attributesDict);
+            CTFontDescriptorCreateCopyWithAttributes(GetDefaultFeaturesDescriptor(), attributesDict);
         CFRelease(attributesDict);
     }
-    
-    aFontRef =
-        CTFontCreateCopyWithAttributes(aFontRef,
-                                       0.0,
-                                       NULL,
-                                       sDisableLigaturesDescriptor);
-    return aFontRef;
+
+    return CTFontCreateWithPlatformFont(aFontRef, aSize, NULL, sDisableLigaturesDescriptor);
 }
 
 void
@@ -759,19 +774,20 @@ gfxCoreTextFontGroup::InitTextRun(gfxTextRun *aTextRun,
     if (disableLigatures) {
         // For letterspacing (or maybe other situations) we need to make a copy of the CTFont
         // with the ligature feature disabled
-        CTFontRef mainCTFont = mainFont->GetCTFont();
-        mainCTFont = gfxCoreTextFont::CreateCopyWithDisabledLigatures(mainCTFont);
+        CTFontRef ctFont =
+            gfxCoreTextFont::CreateCTFontWithDisabledLigatures(mainFont->GetATSFont(),
+                                                               CTFontGetSize(mainFont->GetCTFont()));
 
         // Set up the initial font, for the (common) case of a monostyled textRun
         attrObj =
             CFDictionaryCreate(kCFAllocatorDefault,
                                (const void**) &kCTFontAttributeName,
-                               (const void**) &mainCTFont,
+                               (const void**) &ctFont,
                                1, // count of attributes
                                &kCFTypeDictionaryKeyCallBacks,
                                &kCFTypeDictionaryValueCallBacks);
-        // Having created the dict, we're finished with our modified copy of the CTFont
-        CFRelease(mainCTFont);
+        // Having created the dict, we're finished with our ligature-disabled CTFontRef
+        CFRelease(ctFont);
     } else {
         attrObj = mainFont->GetAttributesDictionary();
         CFRetain(attrObj);
@@ -813,7 +829,8 @@ gfxCoreTextFontGroup::InitTextRun(gfxTextRun *aTextRun,
             if (matchedFont != mainFont) {
                 CTFontRef matchedCTFont = matchedFont->GetCTFont();
                 if (disableLigatures)
-                    matchedCTFont = gfxCoreTextFont::CreateCopyWithDisabledLigatures(matchedCTFont);
+                    matchedCTFont = gfxCoreTextFont::CreateCTFontWithDisabledLigatures(matchedFont->GetATSFont(),
+                                                                                       CTFontGetSize(matchedCTFont));
                 // if necessary, make a mutable copy of the string
                 if (!mutableStringObj) {
                     mutableStringObj =