diff --git a/mozilla/content/base/src/nsGenericDOMDataNode.cpp b/mozilla/content/base/src/nsGenericDOMDataNode.cpp
index 7c2006818d0..001c259f4c2 100644
--- a/mozilla/content/base/src/nsGenericDOMDataNode.cpp
+++ b/mozilla/content/base/src/nsGenericDOMDataNode.cpp
@@ -655,6 +655,11 @@ nsGenericDOMDataNode::SetDocument(nsIDocument* aDocument, PRBool aDeep, PRBool a
         // XXX: Root!
       }
     }
+#ifdef IBMBIDI
+    if (mText.IsBidi()) {
+      mDocument->SetBidiEnabled(PR_TRUE);
+    }
+#endif
   }
 
   return NS_OK;
@@ -961,16 +966,10 @@ nsGenericDOMDataNode::SetText(nsIContent *aOuterContent,
   if (aNotify && (nsnull != mDocument)) {
     mDocument->BeginUpdate();
   }
-#ifdef IBMBIDI
-  if (mDocument != nsnull) {
-    PRBool bidiEnabled = mText.SetTo(aBuffer, aLength);
-    if (bidiEnabled) {
-      mDocument->SetBidiEnabled(PR_TRUE);
-    }
-  }
-  else
-#endif // IBMBIDI
   mText.SetTo(aBuffer, aLength);
+#ifdef IBMBIDI
+  SetBidiStatus();
+#endif // IBMBIDI
 
   if (mDocument && nsGenericElement::HasMutationListeners(aOuterContent, NS_EVENT_BITS_MUTATION_CHARACTERDATAMODIFIED)) {
     nsCOMPtr<nsIDOMEventTarget> node(do_QueryInterface(aOuterContent));
@@ -1045,6 +1044,9 @@ nsGenericDOMDataNode::SetText(nsIContent *aOuterContent,
     mDocument->BeginUpdate();
   }
   mText = aStr;
+#ifdef IBMBIDI
+  SetBidiStatus();
+#endif // IBMBIDI
 
   if (mDocument && nsGenericElement::HasMutationListeners(aOuterContent, NS_EVENT_BITS_MUTATION_CHARACTERDATAMODIFIED)) {
     nsCOMPtr<nsIDOMEventTarget> node(do_QueryInterface(aOuterContent));
@@ -1101,3 +1103,21 @@ nsGenericDOMDataNode::IsOnlyWhitespace(PRBool* aResult)
   *aResult = PR_TRUE;
   return NS_OK;
 }
+
+#ifdef IBMBIDI
+void nsGenericDOMDataNode::SetBidiStatus()
+{
+  PRBool isBidiDocument = PR_FALSE;
+  if (mDocument) {
+    mDocument->GetBidiEnabled(&isBidiDocument);
+    if (isBidiDocument) {
+      // OK, we already know it's Bidi, so we won't test again
+      return;
+    }
+  }
+  mText.SetBidiFlag();
+  if (mDocument && mText.IsBidi()) {
+    mDocument->SetBidiEnabled(PR_TRUE);
+  }
+}
+#endif // IBMBIDI
diff --git a/mozilla/content/base/src/nsGenericDOMDataNode.h b/mozilla/content/base/src/nsGenericDOMDataNode.h
index 5f64c3d3c2e..141bdc4c14b 100644
--- a/mozilla/content/base/src/nsGenericDOMDataNode.h
+++ b/mozilla/content/base/src/nsGenericDOMDataNode.h
@@ -287,6 +287,9 @@ struct nsGenericDOMDataNode {
   //----------------------------------------
 
   void ToCString(nsAWritableString& aBuf, PRInt32 aOffset, PRInt32 aLen) const;
+#ifdef IBMBIDI
+  void SetBidiStatus();
+#endif
 
   nsIDocument* mDocument;
   nsIContent* mParent;
diff --git a/mozilla/content/base/src/nsTextFragment.h b/mozilla/content/base/src/nsTextFragment.h
index 8a857c90aed..34d6c8dc364 100644
--- a/mozilla/content/base/src/nsTextFragment.h
+++ b/mozilla/content/base/src/nsTextFragment.h
@@ -138,6 +138,19 @@ public:
     return mState.mIs2b;
   }
 
+#ifdef IBMBIDI
+  /**
+   * Return PR_TRUE if this fragment contains Bidi text
+   * For performance reasons this flag is not set automatically, but
+   * requires an explicit call to SetBidiFlag()
+   */
+  PRBool IsBidi() const
+  {
+    return mState.mIsBidi;
+  }
+#endif
+
+
   /**
    * Get a pointer to constant PRUnichar data.
    */
@@ -178,7 +191,7 @@ public:
    * buffer. Like operator= except a length is specified instead of
    * assuming 0 termination.
    */
-  PRBool SetTo(const PRUnichar *aBuffer, PRInt32 aLength);
+  void SetTo(const PRUnichar* aBuffer, PRInt32 aLength);
 
   /**
    * Change the contents of this fragment to be a copy of the given
@@ -218,10 +231,19 @@ public:
     return mState.mIs2b ? m2b[aIndex] : PRUnichar(m1b[aIndex]);
   }
 
+#ifdef IBMBIDI
+  /**
+   * Scan the contents of the fragment and turn on mState.mIsBidi if it
+   * includes any Bidi characters.
+   */
+  void SetBidiFlag();
+#endif
+
   struct FragmentBits {
     PRBool mInHeap : 1;
     PRBool mIs2b : 1;
-    PRUint32 mLength : 30;
+    PRBool mIsBidi : 1;
+    PRUint32 mLength : 29;
   };
 
 protected:
diff --git a/mozilla/content/shared/public/nsTextFragment.h b/mozilla/content/shared/public/nsTextFragment.h
index 8a857c90aed..34d6c8dc364 100644
--- a/mozilla/content/shared/public/nsTextFragment.h
+++ b/mozilla/content/shared/public/nsTextFragment.h
@@ -138,6 +138,19 @@ public:
     return mState.mIs2b;
   }
 
+#ifdef IBMBIDI
+  /**
+   * Return PR_TRUE if this fragment contains Bidi text
+   * For performance reasons this flag is not set automatically, but
+   * requires an explicit call to SetBidiFlag()
+   */
+  PRBool IsBidi() const
+  {
+    return mState.mIsBidi;
+  }
+#endif
+
+
   /**
    * Get a pointer to constant PRUnichar data.
    */
@@ -178,7 +191,7 @@ public:
    * buffer. Like operator= except a length is specified instead of
    * assuming 0 termination.
    */
-  PRBool SetTo(const PRUnichar *aBuffer, PRInt32 aLength);
+  void SetTo(const PRUnichar* aBuffer, PRInt32 aLength);
 
   /**
    * Change the contents of this fragment to be a copy of the given
@@ -218,10 +231,19 @@ public:
     return mState.mIs2b ? m2b[aIndex] : PRUnichar(m1b[aIndex]);
   }
 
+#ifdef IBMBIDI
+  /**
+   * Scan the contents of the fragment and turn on mState.mIsBidi if it
+   * includes any Bidi characters.
+   */
+  void SetBidiFlag();
+#endif
+
   struct FragmentBits {
     PRBool mInHeap : 1;
     PRBool mIs2b : 1;
-    PRUint32 mLength : 30;
+    PRBool mIsBidi : 1;
+    PRUint32 mLength : 29;
   };
 
 protected:
diff --git a/mozilla/content/shared/src/nsTextFragment.cpp b/mozilla/content/shared/src/nsTextFragment.cpp
index fe49641d0ab..6e932478221 100644
--- a/mozilla/content/shared/src/nsTextFragment.cpp
+++ b/mozilla/content/shared/src/nsTextFragment.cpp
@@ -167,11 +167,9 @@ nsTextFragment::SetTo(PRUnichar *aBuffer, PRInt32 aLength, PRBool aRelease)
   mState.mLength = aLength;
 }
 
-PRBool
-nsTextFragment::SetTo(const PRUnichar *aBuffer, PRInt32 aLength)
+void
+nsTextFragment::SetTo(const PRUnichar* aBuffer, PRInt32 aLength)
 {
-  PRBool bidiEnabled = PR_FALSE;
-
   ReleaseText();
 
   if (aLength != 0) {
@@ -183,14 +181,7 @@ nsTextFragment::SetTo(const PRUnichar *aBuffer, PRInt32 aLength)
       PRUnichar ch = *ucp++;
       if (ch >> 8) {
         need2 = PR_TRUE;
-#ifdef IBMBIDI
-        if (CHAR_IS_BIDI(ch) ) {
-          bidiEnabled = PR_TRUE;
-#endif // IBMBIDI
         break;
-#ifdef IBMBIDI
-        }
-#endif // IBMBIDI
       }
     }
 
@@ -202,7 +193,7 @@ nsTextFragment::SetTo(const PRUnichar *aBuffer, PRInt32 aLength)
       if (!m2b) {
         NS_ERROR("Failed to clone string buffer!");
 
-        return PR_FALSE;
+        return;
       }
 
       // Setup our fields
@@ -225,7 +216,7 @@ nsTextFragment::SetTo(const PRUnichar *aBuffer, PRInt32 aLength)
         if (!nt) {
           NS_ERROR("Failed to allocate string buffer!");
 
-          return bidiEnabled;
+          return;
         }
 
         // Copy data
@@ -242,8 +233,6 @@ nsTextFragment::SetTo(const PRUnichar *aBuffer, PRInt32 aLength)
       mState.mLength = aLength;
     }
   }
-
-  return bidiEnabled;
 }
 
 void
@@ -337,3 +326,23 @@ nsTextFragment::CopyTo(char *aDest, PRInt32 aOffset, PRInt32 aCount)
     }
   }
 }
+
+#ifdef IBMBIDI
+// To save time we only do this when we really want to know, not during
+// every allocation
+void
+nsTextFragment::SetBidiFlag()
+{
+  if (mState.mIs2b && !mState.mIsBidi) {
+    const PRUnichar* cp = m2b;
+    const PRUnichar* end = cp + mState.mLength;
+    while (cp < end) {
+      PRUnichar ch = *cp++;
+      if (CHAR_IS_BIDI(ch) ) {
+        mState.mIsBidi = PR_TRUE;
+        break;
+      }
+    }
+  }
+}
+#endif