diff --git a/mozilla/content/base/src/nsTextNode.cpp b/mozilla/content/base/src/nsTextNode.cpp
index 81e18734342..e5c3bd035ca 100644
--- a/mozilla/content/base/src/nsTextNode.cpp
+++ b/mozilla/content/base/src/nsTextNode.cpp
@@ -73,6 +73,8 @@ public:
                      PRInt32 aLength,
                      PRBool aNotify);
 
+  NS_IMETHOD IsOnlyWhitespace(PRBool* aResult);
+
 protected:
   nsGenericDOMDataNode mInner;
 };
@@ -298,3 +300,35 @@ nsTextNode::SetText(const char* aBuffer, PRInt32 aLength,
   }
   return NS_OK;
 }
+
+NS_IMETHODIMP
+nsTextNode::IsOnlyWhitespace(PRBool* aResult)
+{
+  nsTextFragment& frag = mInner.mText;
+  if (frag.Is2b()) {
+    const PRUnichar* cp = frag.Get2b();
+    const PRUnichar* end = cp + frag.GetLength();
+    while (cp < end) {
+      PRUnichar ch = *cp++;
+      if (!XP_IS_SPACE(ch)) {
+        *aResult = PR_FALSE;
+        return NS_OK;
+      }
+    }
+  }
+  else {
+    const char* cp = frag.Get1b();
+    const char* end = cp + frag.GetLength();
+    while (cp < end) {
+      PRUnichar ch = PRUnichar(*(unsigned char*)cp);
+      cp++;
+      if (!XP_IS_SPACE(ch)) {
+        *aResult = PR_FALSE;
+        return NS_OK;
+      }
+    }
+  }
+
+  *aResult = PR_TRUE;
+  return NS_OK;
+}
diff --git a/mozilla/layout/base/src/nsTextNode.cpp b/mozilla/layout/base/src/nsTextNode.cpp
index 81e18734342..e5c3bd035ca 100644
--- a/mozilla/layout/base/src/nsTextNode.cpp
+++ b/mozilla/layout/base/src/nsTextNode.cpp
@@ -73,6 +73,8 @@ public:
                      PRInt32 aLength,
                      PRBool aNotify);
 
+  NS_IMETHOD IsOnlyWhitespace(PRBool* aResult);
+
 protected:
   nsGenericDOMDataNode mInner;
 };
@@ -298,3 +300,35 @@ nsTextNode::SetText(const char* aBuffer, PRInt32 aLength,
   }
   return NS_OK;
 }
+
+NS_IMETHODIMP
+nsTextNode::IsOnlyWhitespace(PRBool* aResult)
+{
+  nsTextFragment& frag = mInner.mText;
+  if (frag.Is2b()) {
+    const PRUnichar* cp = frag.Get2b();
+    const PRUnichar* end = cp + frag.GetLength();
+    while (cp < end) {
+      PRUnichar ch = *cp++;
+      if (!XP_IS_SPACE(ch)) {
+        *aResult = PR_FALSE;
+        return NS_OK;
+      }
+    }
+  }
+  else {
+    const char* cp = frag.Get1b();
+    const char* end = cp + frag.GetLength();
+    while (cp < end) {
+      PRUnichar ch = PRUnichar(*(unsigned char*)cp);
+      cp++;
+      if (!XP_IS_SPACE(ch)) {
+        *aResult = PR_FALSE;
+        return NS_OK;
+      }
+    }
+  }
+
+  *aResult = PR_TRUE;
+  return NS_OK;
+}