diff --git a/dom/xml/nsXMLContentSink.cpp b/dom/xml/nsXMLContentSink.cpp
index e325f8f6faa..2562fe84416 100644
--- a/dom/xml/nsXMLContentSink.cpp
+++ b/dom/xml/nsXMLContentSink.cpp
@@ -96,8 +96,7 @@ NS_NewXMLContentSink(nsIXMLContentSink** aResult,
 }
 
 nsXMLContentSink::nsXMLContentSink()
-  : mConstrainSize(true),
-    mPrettyPrintXML(true)
+  : mPrettyPrintXML(true)
 {
 }
 
@@ -475,7 +474,6 @@ nsXMLContentSink::CreateElement(const char16_t** aAtts, uint32_t aAttsCount,
     nsCOMPtr<nsIScriptElement> sele = do_QueryInterface(content);
     sele->SetScriptLineNumber(aLineNumber);
     sele->SetCreatorParser(GetParser());
-    mConstrainSize = false;
   }
 
   // XHTML needs some special attention
@@ -552,7 +550,6 @@ nsXMLContentSink::CloseElement(nsIContent* aContent)
   if (nodeInfo->Equals(nsGkAtoms::script, kNameSpaceID_XHTML)
       || nodeInfo->Equals(nsGkAtoms::script, kNameSpaceID_SVG)
     ) {
-    mConstrainSize = true;
     nsCOMPtr<nsIScriptElement> sele = do_QueryInterface(aContent);
 
     if (mPreventScriptExecution) {
@@ -778,26 +775,19 @@ nsXMLContentSink::FlushText(bool aReleaseTextNode)
 
   if (mTextLength != 0) {
     if (mLastTextNode) {
-      if ((mLastTextNodeSize + mTextLength) > mTextSize && !mXSLTProcessor) {
-        mLastTextNodeSize = 0;
-        mLastTextNode = nullptr;
-        FlushText(aReleaseTextNode);
-      } else {
-        bool notify = HaveNotifiedForCurrentContent();
-        // We could probably always increase mInNotification here since
-        // if AppendText doesn't notify it shouldn't trigger evil code.
-        // But just in case it does, we don't want to mask any notifications.
-        if (notify) {
-          ++mInNotification;
-        }
-        rv = mLastTextNode->AppendText(mText, mTextLength, notify);
-        if (notify) {
-          --mInNotification;
-        }
-
-        mLastTextNodeSize += mTextLength;
-        mTextLength = 0;
+      bool notify = HaveNotifiedForCurrentContent();
+      // We could probably always increase mInNotification here since
+      // if AppendText doesn't notify it shouldn't trigger evil code.
+      // But just in case it does, we don't want to mask any notifications.
+      if (notify) {
+        ++mInNotification;
       }
+      rv = mLastTextNode->AppendText(mText, mTextLength, notify);
+      if (notify) {
+        --mInNotification;
+      }
+
+      mTextLength = 0;
     } else {
       nsRefPtr<nsTextNode> textContent = new nsTextNode(mNodeInfoManager);
 
@@ -805,7 +795,6 @@ nsXMLContentSink::FlushText(bool aReleaseTextNode)
 
       // Set the text in the text node
       textContent->SetText(mText, mTextLength, false);
-      mLastTextNodeSize += mTextLength;
       mTextLength = 0;
 
       // Add text to its parent
@@ -814,7 +803,6 @@ nsXMLContentSink::FlushText(bool aReleaseTextNode)
   }
 
   if (aReleaseTextNode) {
-    mLastTextNodeSize = 0;
     mLastTextNode = nullptr;
   }
 
@@ -1446,40 +1434,20 @@ nsXMLContentSink::AddText(const char16_t* aText,
     mTextSize = NS_ACCUMULATION_BUFFER_SIZE;
   }
 
-  // Copy data from string into our buffer; flush buffer when it fills up
-  int32_t offset = 0;
-  while (0 != aLength) {
-    int32_t amount = mTextSize - mTextLength;
-    if (0 == amount) {
-      // XSLT wants adjacent textnodes merged.
-      if (mConstrainSize && !mXSLTProcessor) {
-        nsresult rv = FlushText();
-        if (NS_OK != rv) {
-          return rv;
-        }
+  // Copy data from string into our buffer, resizing the buffer if
+  // it's not big enough.
+  int32_t availableSpace = mTextSize - mTextLength;
+  if (availableSpace < aLength) {
+    mTextSize = mTextLength + aLength;
+    mText = (char16_t *) PR_REALLOC(mText, sizeof(char16_t) * mTextSize);
+    if (nullptr == mText) {
+      mTextSize = 0;
 
-        amount = mTextSize - mTextLength;
-      }
-      else {
-        mTextSize += aLength;
-        mText = (char16_t *) PR_REALLOC(mText, sizeof(char16_t) * mTextSize);
-        if (nullptr == mText) {
-          mTextSize = 0;
-
-          return NS_ERROR_OUT_OF_MEMORY;
-        }
-
-        amount = aLength;
-      }
+      return NS_ERROR_OUT_OF_MEMORY;
     }
-    if (amount > aLength) {
-      amount = aLength;
-    }
-    memcpy(&mText[mTextLength], &aText[offset], sizeof(char16_t) * amount);
-    mTextLength += amount;
-    offset += amount;
-    aLength -= amount;
   }
+  memcpy(&mText[mTextLength], aText, sizeof(char16_t) * aLength);
+  mTextLength += aLength;
 
   return NS_OK;
 }
diff --git a/dom/xml/nsXMLContentSink.h b/dom/xml/nsXMLContentSink.h
index 7ec23dba21d..f39f0039591 100644
--- a/dom/xml/nsXMLContentSink.h
+++ b/dom/xml/nsXMLContentSink.h
@@ -180,9 +180,7 @@ protected:
   
   int32_t mNotifyLevel;
   nsCOMPtr<nsIContent> mLastTextNode;
-  int32_t mLastTextNodeSize;
 
-  uint8_t mConstrainSize : 1;
   uint8_t mPrettyPrintXML : 1;
   uint8_t mPrettyPrintHasSpecialRoot : 1;
   uint8_t mPrettyPrintHasFactoredElements : 1;