--- a/dom/base/nsDocumentEncoder.cpp
+++ b/dom/base/nsDocumentEncoder.cpp
@@ -41,16 +41,17 @@
 #include "nsITransferable.h" // for kUnicodeMime
 #include "nsContentUtils.h"
 #include "nsNodeUtils.h"
 #include "nsUnicharUtils.h"
 #include "nsReadableUtils.h"
 #include "nsTArray.h"
 #include "nsIFrame.h"
 #include "nsStringBuffer.h"
+#include "mozilla/AutoRestore.h"
 #include "mozilla/dom/Element.h"
 #include "mozilla/dom/ShadowRoot.h"
 #include "mozilla/dom/EncodingUtils.h"
 #include "nsLayoutUtils.h"
 
 using namespace mozilla;
 using namespace mozilla::dom;
 
@@ -137,16 +138,35 @@ protected:
           return false;
       }
     }
     return true;
   }
 
   virtual bool IncludeInContext(nsINode *aNode);
 
+  class MOZ_STACK_CLASS AutoReleaseDocumentIfNeeded final
+  {
+  public:
+    AutoReleaseDocumentIfNeeded(nsDocumentEncoder* aEncoder)
+      : mEncoder(aEncoder)
+    {
+    }
+
+    ~AutoReleaseDocumentIfNeeded()
+    {
+      if (mEncoder->mFlags & ReleaseDocumentAfterOutput) {
+        mEncoder->mDocument = nullptr;
+      }
+    }
+
+  private:
+    nsDocumentEncoder* mEncoder;
+  };
+
   nsCOMPtr<nsIDocument>          mDocument;
   nsCOMPtr<nsISelection>         mSelection;
   RefPtr<nsRange>              mRange;
   nsCOMPtr<nsINode>              mNode;
   nsCOMPtr<nsIOutputStream>      mStream;
   nsCOMPtr<nsIContentSerializer> mSerializer;
   nsCOMPtr<nsIUnicodeEncoder>    mUnicodeEncoder;
   nsCOMPtr<nsINode>              mCommonParent;
@@ -1004,16 +1024,18 @@ nsDocumentEncoder::EncodeToString(nsAStr
 
 NS_IMETHODIMP
 nsDocumentEncoder::EncodeToStringWithMaxLength(uint32_t aMaxLength,
                                                nsAString& aOutputString)
 {
   if (!mDocument)
     return NS_ERROR_NOT_INITIALIZED;
 
+  AutoReleaseDocumentIfNeeded autoReleaseDocument(this);
+
   aOutputString.Truncate();
 
   nsString output;
   static const size_t bufferSize = 2048;
   if (!mCachedBuffer) {
     mCachedBuffer = nsStringBuffer::Alloc(bufferSize).take();
     if (NS_WARN_IF(!mCachedBuffer)) {
       return NS_ERROR_OUT_OF_MEMORY;

--- a/dom/base/nsIDocumentEncoder.idl
+++ b/dom/base/nsIDocumentEncoder.idl
@@ -243,16 +243,23 @@ interface nsIDocumentEncoder : nsISuppor
   /**
    * Disallow breaking of long character strings. This is important
    * for serializing e-mail which contains CJK strings. These must
    * not be broken just as "normal" longs strings aren't broken.
    */
   const unsigned long OutputDisallowLineBreaking = (1 << 27);
 
   /**
+   * Release reference of nsIDocument after using encodeTo* method to recycle
+   * this encoder without holding nsIDocument. To use this encoder again,
+   * we have to call init again.
+   */
+  const unsigned long ReleaseDocumentAfterOutput = (1 << 28);
+
+  /**
    * Initialize with a pointer to the document and the mime type.
    * @param aDocument Document to encode.
    * @param aMimeType MimeType to use. May also be set by SetMimeType.
    * @param aFlags Flags to use while encoding. May also be set by SetFlags.
    */
   void init(in nsIDOMDocument aDocument,
             in AString aMimeType,
             in unsigned long aFlags);