diff --git a/gfx/thebes/gfxFont.cpp b/gfx/thebes/gfxFont.cpp
index a11296d097a..23b98b9684d 100644
--- a/gfx/thebes/gfxFont.cpp
+++ b/gfx/thebes/gfxFont.cpp
@@ -1300,96 +1300,34 @@ gfxFont::Measure(gfxTextRun *aTextRun,
     return metrics;
 }
 
-#define MAX_SHAPING_LENGTH  32760 // slightly less than 32K, trying to avoid
-                                  // over-stressing platform shapers
-
-#define BACKTRACK_LIMIT  1024 // If we can't find a space or a cluster start
-                              // within 1K chars, just chop arbitrarily.
-                              // Limiting backtrack here avoids pathological
-                              // behavior on long runs with no whitespace.
-
 PRBool
 gfxFont::InitTextRun(gfxContext *aContext,
                      gfxTextRun *aTextRun,
                      const PRUnichar *aString,
                      PRUint32 aRunStart,
                      PRUint32 aRunLength,
-                     PRInt32 aRunScript,
-                     PRBool aPreferPlatformShaping)
+                     PRInt32 aRunScript)
 {
-    PRBool ok;
+    PRBool ok = PR_FALSE;
 
-    do {
-        // Because various shaping backends struggle with very long runs,
-        // we look for appropriate break locations (preferring whitespace),
-        // and shape sub-runs of no more than 32K characters at a time.
-        // See bug 606714 (CoreText), and similar Uniscribe issues.
-        // This loop always executes at least once, and "processes" up to
-        // MAX_RUN_LENGTH_FOR_SHAPING characters, updating aRunStart and
-        // aRunLength accordingly. It terminates when the entire run has
-        // been processed, or when shaping fails.
-
-        PRUint32 thisRunLength;
-        ok = PR_FALSE;
-
-        if (aRunLength <= MAX_SHAPING_LENGTH) {
-            thisRunLength = aRunLength;
-        } else {
-            // We're splitting this font run because it's very long
-            PRUint32 offset = aRunStart + MAX_SHAPING_LENGTH;
-            PRUint32 clusterStart = 0;
-            while (offset > aRunStart + MAX_SHAPING_LENGTH - BACKTRACK_LIMIT) {
-                if (aTextRun->IsClusterStart(offset)) {
-                    if (!clusterStart) {
-                        clusterStart = offset;
-                    }
-                    if (aString[offset] == ' ' || aString[offset - 1] == ' ') {
-                        break;
-                    }
-                }
-                --offset;
-            }
-            
-            if (offset > MAX_SHAPING_LENGTH - BACKTRACK_LIMIT) {
-                // we found a space, so break the run there
-                thisRunLength = offset - aRunStart;
-            } else if (clusterStart != 0) {
-                // didn't find a space, but we found a cluster start
-                thisRunLength = clusterStart - aRunStart;
-            } else {
-                // otherwise we'll simply break at MAX_SHAPING_LENGTH chars,
-                // which may interfere with shaping behavior (but in practice
-                // only pathological cases will lack ANY whitespace or cluster
-                // boundaries, so we don't really care; it won't affect any
-                // "real" text)
-                thisRunLength = MAX_SHAPING_LENGTH;
-            }
+    if (mHarfBuzzShaper) {
+        if (gfxPlatform::GetPlatform()->UseHarfBuzzLevel() >=
+            gfxUnicodeProperties::ScriptShapingLevel(aRunScript)) {
+            ok = mHarfBuzzShaper->InitTextRun(aContext, aTextRun, aString,
+                                              aRunStart, aRunLength, aRunScript);
         }
+    }
 
-        if (mHarfBuzzShaper && !aPreferPlatformShaping) {
-            if (gfxPlatform::GetPlatform()->UseHarfBuzzLevel() >=
-                gfxUnicodeProperties::ScriptShapingLevel(aRunScript)) {
-                ok = mHarfBuzzShaper->InitTextRun(aContext, aTextRun, aString,
-                                                  aRunStart, thisRunLength,
-                                                  aRunScript);
-            }
+    if (!ok) {
+        if (!mPlatformShaper) {
+            CreatePlatformShaper();
+            NS_ASSERTION(mPlatformShaper, "no platform shaper available!");
         }
-
-        if (!ok) {
-            if (!mPlatformShaper) {
-                CreatePlatformShaper();
-                NS_ASSERTION(mPlatformShaper, "no platform shaper available!");
-            }
-            if (mPlatformShaper) {
-                ok = mPlatformShaper->InitTextRun(aContext, aTextRun, aString,
-                                                  aRunStart, thisRunLength,
-                                                  aRunScript);
-            }
+        if (mPlatformShaper) {
+            ok = mPlatformShaper->InitTextRun(aContext, aTextRun, aString,
+                                              aRunStart, aRunLength, aRunScript);
         }
-        
-        aRunStart += thisRunLength;
-        aRunLength -= thisRunLength;
-    } while (ok && aRunLength > 0);
+    }
 
     NS_WARN_IF_FALSE(ok, "shaper failed, expect scrambled or missing text");
     return ok;
diff --git a/gfx/thebes/gfxFont.h b/gfx/thebes/gfxFont.h
index 980dc39b8e4..3b9fd312169 100644
--- a/gfx/thebes/gfxFont.h
+++ b/gfx/thebes/gfxFont.h
@@ -1136,8 +1136,7 @@ public:
                                const PRUnichar *aString,
                                PRUint32 aRunStart,
                                PRUint32 aRunLength,
-                               PRInt32 aRunScript,
-                               PRBool aPreferPlatformShaping = PR_FALSE);
+                               PRInt32 aRunScript);
 
 protected:
     nsRefPtr<gfxFontEntry> mFontEntry;
diff --git a/gfx/thebes/gfxGDIFont.cpp b/gfx/thebes/gfxGDIFont.cpp
index ff7e84c4e7b..1181f9fcd97 100644
--- a/gfx/thebes/gfxGDIFont.cpp
+++ b/gfx/thebes/gfxGDIFont.cpp
@@ -142,8 +142,7 @@ gfxGDIFont::InitTextRun(gfxContext *aContext,
                         const PRUnichar *aString,
                         PRUint32 aRunStart,
                         PRUint32 aRunLength,
-                        PRInt32 aRunScript,
-                        PRBool aPreferPlatformShaping)
+                        PRInt32 aRunScript)
 {
     if (!mMetrics) {
         Initialize();
diff --git a/gfx/thebes/gfxGDIFont.h b/gfx/thebes/gfxGDIFont.h
index b1366bc14a9..4c2cc5563ef 100644
--- a/gfx/thebes/gfxGDIFont.h
+++ b/gfx/thebes/gfxGDIFont.h
@@ -82,8 +82,7 @@ public:
                                const PRUnichar *aString,
                                PRUint32 aRunStart,
                                PRUint32 aRunLength,
-                               PRInt32 aRunScript,
-                               PRBool aPreferPlatformShaping = PR_FALSE);
+                               PRInt32 aRunScript);
 
     virtual PRBool ProvidesHintedWidths() const { return PR_TRUE; }
 
diff --git a/gfx/thebes/gfxMacFont.cpp b/gfx/thebes/gfxMacFont.cpp
index 1da12ab6175..57445baf223 100644
--- a/gfx/thebes/gfxMacFont.cpp
+++ b/gfx/thebes/gfxMacFont.cpp
@@ -159,17 +159,54 @@ gfxMacFont::InitTextRun(gfxContext *aContext,
                         const PRUnichar *aString,
                         PRUint32 aRunStart,
                         PRUint32 aRunLength,
-                        PRInt32 aRunScript,
-                        PRBool aPreferPlatformShaping)
+                        PRInt32 aRunScript)
 {
     if (!mIsValid) {
         NS_WARNING("invalid font! expect incorrect text rendering");
         return PR_FALSE;
     }
 
-    PRBool ok = gfxFont::InitTextRun(aContext, aTextRun, aString,
-                                     aRunStart, aRunLength, aRunScript,
-        static_cast<MacOSFontEntry*>(GetFontEntry())->RequiresAATLayout());
+    PRBool ok = PR_FALSE;
+
+    if (mHarfBuzzShaper &&
+        !static_cast<MacOSFontEntry*>(GetFontEntry())->RequiresAATLayout())
+    {
+        if (gfxPlatform::GetPlatform()->UseHarfBuzzLevel() >=
+            gfxUnicodeProperties::ScriptShapingLevel(aRunScript)) {
+            ok = mHarfBuzzShaper->InitTextRun(aContext, aTextRun, aString,
+                                              aRunStart, aRunLength, 
+                                              aRunScript);
+#if DEBUG
+            if (!ok) {
+                NS_ConvertUTF16toUTF8 name(GetName());
+                char msg[256];
+                sprintf(msg, "HarfBuzz shaping failed for font: %s",
+                        name.get());
+                NS_WARNING(msg);
+            }
+#endif
+        }
+    }
+
+    if (!ok) {
+        // fallback to Core Text shaping
+        if (!mPlatformShaper) {
+            CreatePlatformShaper();
+        }
+
+        ok = mPlatformShaper->InitTextRun(aContext, aTextRun, aString,
+                                          aRunStart, aRunLength, 
+                                          aRunScript);
+#if DEBUG
+        if (!ok) {
+            NS_ConvertUTF16toUTF8 name(GetName());
+            char msg[256];
+            sprintf(msg, "Core Text shaping failed for font: %s",
+                    name.get());
+            NS_WARNING(msg);
+        }
+#endif
+    }
 
     aTextRun->AdjustAdvancesForSyntheticBold(aRunStart, aRunLength);
 
diff --git a/gfx/thebes/gfxMacFont.h b/gfx/thebes/gfxMacFont.h
index 4d8a9957f81..b1320c980f1 100644
--- a/gfx/thebes/gfxMacFont.h
+++ b/gfx/thebes/gfxMacFont.h
@@ -62,8 +62,7 @@ public:
                                const PRUnichar *aString,
                                PRUint32 aRunStart,
                                PRUint32 aRunLength,
-                               PRInt32 aRunScript,
-                               PRBool aPreferPlatformShaping = PR_FALSE);
+                               PRInt32 aRunScript);
 
     /* overrides for the pure virtual methods in gfxFont */
     virtual const gfxFont::Metrics& GetMetrics() {