diff --git a/dom/xslt/xslt/txMozillaStylesheetCompiler.cpp b/dom/xslt/xslt/txMozillaStylesheetCompiler.cpp
index eaf27c3a4e42..e57de68da8ef 100644
--- a/dom/xslt/xslt/txMozillaStylesheetCompiler.cpp
+++ b/dom/xslt/xslt/txMozillaStylesheetCompiler.cpp
@@ -630,8 +630,7 @@ txSyncCompileObserver::loadURI(const nsAString& aUri,
     // make sense.
     nsCOMPtr<nsINode> source;
     if (mProcessor) {
-      source =
-        do_QueryInterface(mProcessor->GetSourceContentModel());
+      source = mProcessor->GetSourceContentModel();
     }
     nsAutoSyncOperation sync(source ? source->OwnerDoc() : nullptr);
     nsCOMPtr<nsIDOMDocument> document;
diff --git a/dom/xslt/xslt/txMozillaTextOutput.cpp b/dom/xslt/xslt/txMozillaTextOutput.cpp
index 4644194e089c..db65131ee8c5 100644
--- a/dom/xslt/xslt/txMozillaTextOutput.cpp
+++ b/dom/xslt/xslt/txMozillaTextOutput.cpp
@@ -121,7 +121,7 @@ txMozillaTextOutput::startDocument()
 }
 
 nsresult
-txMozillaTextOutput::createResultDocument(nsIDOMDocument* aSourceDocument,
+txMozillaTextOutput::createResultDocument(nsIDocument* aSourceDocument,
                                           bool aLoadedAsData)
 {
     /*
@@ -148,17 +148,15 @@ txMozillaTextOutput::createResultDocument(nsIDOMDocument* aSourceDocument,
     MOZ_ASSERT(mDocument->GetReadyStateEnum() ==
                nsIDocument::READYSTATE_UNINITIALIZED, "Bad readyState");
     mDocument->SetReadyStateInternal(nsIDocument::READYSTATE_LOADING);
-    nsCOMPtr<nsIDocument> source = do_QueryInterface(aSourceDocument);
-    NS_ENSURE_STATE(source);
     bool hasHadScriptObject = false;
     nsIScriptGlobalObject* sgo =
-      source->GetScriptHandlingObject(hasHadScriptObject);
+      aSourceDocument->GetScriptHandlingObject(hasHadScriptObject);
     NS_ENSURE_STATE(sgo || !hasHadScriptObject);
 
     NS_ASSERTION(mDocument, "Need document");
 
     // Reset and set up document
-    URIUtils::ResetWithSource(mDocument, source);
+    URIUtils::ResetWithSource(mDocument, aSourceDocument);
     // Only do this after resetting the document to ensure we have the
     // correct principal.
     mDocument->SetScriptHandlingObject(sgo);
diff --git a/dom/xslt/xslt/txMozillaTextOutput.h b/dom/xslt/xslt/txMozillaTextOutput.h
index 4520dce3921d..e1c84640e65d 100644
--- a/dom/xslt/xslt/txMozillaTextOutput.h
+++ b/dom/xslt/xslt/txMozillaTextOutput.h
@@ -11,7 +11,6 @@
 #include "nsWeakPtr.h"
 #include "txOutputFormat.h"
 
-class nsIDOMDocument;
 class nsIDOMDocumentFragment;
 class nsITransformObserver;
 class nsIDocument;
@@ -27,7 +26,7 @@ public:
     TX_DECL_TXAXMLEVENTHANDLER
     TX_DECL_TXAOUTPUTXMLEVENTHANDLER
 
-    nsresult createResultDocument(nsIDOMDocument* aSourceDocument,
+    nsresult createResultDocument(nsIDocument* aSourceDocument,
                                   bool aLoadedAsData);
 
 private:
diff --git a/dom/xslt/xslt/txMozillaXMLOutput.cpp b/dom/xslt/xslt/txMozillaXMLOutput.cpp
index baa9a87513cc..f69b8185629e 100644
--- a/dom/xslt/xslt/txMozillaXMLOutput.cpp
+++ b/dom/xslt/xslt/txMozillaXMLOutput.cpp
@@ -777,7 +777,7 @@ void txMozillaXMLOutput::processHTTPEquiv(nsAtom* aHeader, const nsString& aValu
 
 nsresult
 txMozillaXMLOutput::createResultDocument(const nsAString& aName, int32_t aNsID,
-                                         nsIDOMDocument* aSourceDocument,
+                                         nsIDocument* aSourceDocument,
                                          bool aLoadedAsData)
 {
     nsresult rv;
@@ -800,18 +800,16 @@ txMozillaXMLOutput::createResultDocument(const nsAString& aName, int32_t aNsID,
                nsIDocument::READYSTATE_UNINITIALIZED, "Bad readyState");
     mDocument->SetReadyStateInternal(nsIDocument::READYSTATE_LOADING);
     mDocument->SetMayStartLayout(false);
-    nsCOMPtr<nsIDocument> source = do_QueryInterface(aSourceDocument);
-    NS_ENSURE_STATE(source);
     bool hasHadScriptObject = false;
     nsIScriptGlobalObject* sgo =
-      source->GetScriptHandlingObject(hasHadScriptObject);
+      aSourceDocument->GetScriptHandlingObject(hasHadScriptObject);
     NS_ENSURE_STATE(sgo || !hasHadScriptObject);
 
     mCurrentNode = mDocument;
     mNodeInfoManager = mDocument->NodeInfoManager();
 
     // Reset and set up the document
-    URIUtils::ResetWithSource(mDocument, source);
+    URIUtils::ResetWithSource(mDocument, aSourceDocument);
 
     // Make sure we set the script handling object after resetting with the
     // source, so that we have the right principal.
diff --git a/dom/xslt/xslt/txMozillaXMLOutput.h b/dom/xslt/xslt/txMozillaXMLOutput.h
index e748e3f284e1..7cc1beb076e9 100644
--- a/dom/xslt/xslt/txMozillaXMLOutput.h
+++ b/dom/xslt/xslt/txMozillaXMLOutput.h
@@ -73,7 +73,7 @@ public:
     nsresult closePrevious(bool aFlushText);
 
     nsresult createResultDocument(const nsAString& aName, int32_t aNsID,
-                                  nsIDOMDocument* aSourceDocument,
+                                  nsIDocument* aSourceDocument,
                                   bool aLoadedAsData);
 
 private:
diff --git a/dom/xslt/xslt/txMozillaXSLTProcessor.cpp b/dom/xslt/xslt/txMozillaXSLTProcessor.cpp
index 06bd0d08b515..fd7f26f2c336 100644
--- a/dom/xslt/xslt/txMozillaXSLTProcessor.cpp
+++ b/dom/xslt/xslt/txMozillaXSLTProcessor.cpp
@@ -50,7 +50,7 @@ class txToDocHandlerFactory : public txAOutputHandlerFactory
 {
 public:
     txToDocHandlerFactory(txExecutionState* aEs,
-                          nsIDOMDocument* aSourceDocument,
+                          nsIDocument* aSourceDocument,
                           nsITransformObserver* aObserver,
                           bool aDocumentIsData)
         : mEs(aEs), mSourceDocument(aSourceDocument), mObserver(aObserver),
@@ -62,7 +62,7 @@ public:
 
 private:
     txExecutionState* mEs;
-    nsCOMPtr<nsIDOMDocument> mSourceDocument;
+    nsCOMPtr<nsIDocument> mSourceDocument;
     nsCOMPtr<nsITransformObserver> mObserver;
     bool mDocumentIsData;
 };
@@ -664,14 +664,12 @@ txMozillaXSLTProcessor::TransformToDoc(nsIDOMDocument **aResult,
         return NS_ERROR_OUT_OF_MEMORY;
     }
 
-    nsCOMPtr<nsIDOMDocument> sourceDOMDocument = do_QueryInterface(mSource->OwnerDoc());
-
     txExecutionState es(mStylesheet, IsLoadDisabled());
 
     // XXX Need to add error observers
 
     // If aResult is non-null, we're a data document
-    txToDocHandlerFactory handlerFactory(&es, sourceDOMDocument, mObserver,
+    txToDocHandlerFactory handlerFactory(&es, mSource->OwnerDoc(), mObserver,
                                          aCreateDataDocument);
     es.mOutputHandlerFactory = &handlerFactory;