diff --git a/dom/base/DOMParser.cpp b/dom/base/DOMParser.cpp
index bf4ce4f6680c..ee5a2dc34b8d 100644
--- a/dom/base/DOMParser.cpp
+++ b/dom/base/DOMParser.cpp
@@ -28,7 +28,7 @@ using namespace mozilla::dom;
 
 DOMParser::DOMParser()
   : mAttemptedInit(false)
-  , mOriginalPrincipalWasSystem(false)
+  , mForceEnableXULXBL(false)
 {
 }
 
@@ -95,7 +95,7 @@ DOMParser::ParseFromString(const nsAString& str,
 
     // Keep the XULXBL state in sync with the XML case.
 
-    if (mOriginalPrincipalWasSystem) {
+    if (mForceEnableXULXBL) {
       document->ForceEnableXULXBL();
     }
 
@@ -262,7 +262,7 @@ DOMParser::ParseFromStream(nsIInputStream* aStream,
 
   // Keep the XULXBL state in sync with the HTML case
 
-  if (mOriginalPrincipalWasSystem) {
+  if (mForceEnableXULXBL) {
     document->ForceEnableXULXBL();
   }
 
@@ -345,7 +345,7 @@ DOMParser::Init(nsIPrincipal* principal, nsIURI* documentURI,
     if (nsContentUtils::IsSystemPrincipal(mPrincipal)) {
       // Don't give DOMParsers the system principal.  Use a null
       // principal instead.
-      mOriginalPrincipalWasSystem = true;
+      mForceEnableXULXBL = true;
       mPrincipal = NullPrincipal::CreateWithoutOriginAttributes();
 
       if (!mDocumentURI) {
@@ -410,20 +410,6 @@ DOMParser::InitInternal(nsISupports* aOwner, nsIPrincipal* prin,
   return Init(prin, documentURI, baseURI, scriptglobal);
 }
 
-void
-DOMParser::Init(nsIPrincipal* aPrincipal, nsIURI* aDocumentURI,
-                nsIURI* aBaseURI, mozilla::ErrorResult& rv)
-{
-  AttemptedInitMarker marker(&mAttemptedInit);
-
-  nsCOMPtr<nsIPrincipal> principal = aPrincipal;
-  if (!principal && !aDocumentURI) {
-    principal = nsContentUtils::SubjectPrincipal();
-  }
-
-  rv = Init(principal, aDocumentURI, aBaseURI, GetEntryGlobal());
-}
-
 nsresult
 DOMParser::SetUpDocument(DocumentFlavor aFlavor, nsIDOMDocument** aResult)
 {
diff --git a/dom/base/DOMParser.h b/dom/base/DOMParser.h
index d1656a6c346e..db1b88507dd0 100644
--- a/dom/base/DOMParser.h
+++ b/dom/base/DOMParser.h
@@ -63,8 +63,11 @@ public:
                   int32_t aContentLength, mozilla::dom::SupportedType aType,
                   mozilla::ErrorResult& rv);
 
-  void Init(nsIPrincipal* aPrincipal, nsIURI* aDocumentURI,
-            nsIURI* aBaseURI, mozilla::ErrorResult& rv);
+  void
+  ForceEnableXULXBL()
+  {
+    mForceEnableXULXBL = true;
+  }
 
   nsISupports* GetParentObject() const
   {
@@ -80,7 +83,7 @@ private:
   explicit DOMParser(nsISupports* aOwner)
     : mOwner(aOwner)
     , mAttemptedInit(false)
-    , mOriginalPrincipalWasSystem(false)
+    , mForceEnableXULXBL(false)
   {
     MOZ_ASSERT(aOwner);
   }
@@ -140,7 +143,7 @@ private:
   nsWeakPtr mScriptHandlingObject;
 
   bool mAttemptedInit;
-  bool mOriginalPrincipalWasSystem;
+  bool mForceEnableXULXBL;
 };
 
 } // namespace dom
diff --git a/dom/base/test/chrome/test_domparsing.xul b/dom/base/test/chrome/test_domparsing.xul
index 7e9ead3aeb83..9b2ab439110b 100644
--- a/dom/base/test/chrome/test_domparsing.xul
+++ b/dom/base/test/chrome/test_domparsing.xul
@@ -37,13 +37,6 @@ new DOMParser(0);
 new DOMParser("");
 new DOMParser({});
 
-{
-  let parser = new DOMParser();
-  throws(function() {
-    parser.init();
-  }, "NS_ERROR_UNEXPECTED", "init method should throw when DOMParser is created by constructor");
-}
-
 // XMLSerializer constructor should not throw for extra arguments
 new XMLSerializer(undefined);
 new XMLSerializer(null);
@@ -54,15 +47,6 @@ new XMLSerializer({});
 
 runTest(new DOMParser(), new XMLSerializer());
 
-{
-  let parser = Cc["@mozilla.org/xmlextras/domparser;1"]
-               .createInstance(Ci.nsIDOMParser);
-  parser.init();
-  throws(function() {
-    parser.init();
-  }, "NS_ERROR_UNEXPECTED", "init method should throw when called twice");
-}
-
 runTest(Cc["@mozilla.org/xmlextras/domparser;1"]
         .createInstance(Ci.nsIDOMParser),
         new XMLSerializer());
@@ -71,7 +55,6 @@ function runTest(parser, serializer) {
   is(typeof parser.parseFromString, "function", "parseFromString should exist");
   is(typeof parser.parseFromBuffer, "function", "parseFromBuffer should exist");
   is(typeof parser.parseFromStream, "function", "parseFromStream should exist");
-  is(typeof parser.init, "function", "init should exist");
 
   is(typeof serializer.serializeToString, "function", "serializeToString should exist");
   is(typeof serializer.serializeToStream, "function", "serializeToStream should exist");
diff --git a/dom/base/test/unit/head_xml.js b/dom/base/test/unit/head_xml.js
index e5db03e8e0e7..55bf5fcca2a8 100644
--- a/dom/base/test/unit/head_xml.js
+++ b/dom/base/test/unit/head_xml.js
@@ -22,7 +22,7 @@ Cu.importGlobalProperties(["XMLSerializer"]);
 
 function DOMParser() {
   var parser = C["@mozilla.org/xmlextras/domparser;1"].createInstance(nsIDOMParser);
-  parser.init();
+  parser.forceEnableXULXBL();
   return parser;
 }
 
diff --git a/dom/base/test/unit/test_cancelPrefetch.js b/dom/base/test/unit/test_cancelPrefetch.js
index 7e67e40fa8ca..54f2040cef03 100644
--- a/dom/base/test/unit/test_cancelPrefetch.js
+++ b/dom/base/test/unit/test_cancelPrefetch.js
@@ -21,7 +21,6 @@ var node2;
 function run_test() {
   prefs.setBoolPref("network.prefetch-next", true);
 
-  parser.init();
   doc = parser.parseFromString(docbody, "text/html");
 
   node1 = doc.getElementById("node1");
diff --git a/dom/base/test/unit/test_xhr_document.js b/dom/base/test/unit/test_xhr_document.js
index 81ab512a8906..24a21a8a5115 100644
--- a/dom/base/test/unit/test_xhr_document.js
+++ b/dom/base/test/unit/test_xhr_document.js
@@ -22,7 +22,6 @@ function run_test() {
   server.registerPathHandler("/foo", handler);
 
   var parser = Cc["@mozilla.org/xmlextras/domparser;1"].createInstance(Ci.nsIDOMParser);
-  parser.init();
   let doc = parser.parseFromString(docbody, "text/html");
   let xhr = new XMLHttpRequest();
   xhr.onload = function() {
diff --git a/dom/webidl/DOMParser.webidl b/dom/webidl/DOMParser.webidl
index f81460626dcb..f608ee45d147 100644
--- a/dom/webidl/DOMParser.webidl
+++ b/dom/webidl/DOMParser.webidl
@@ -36,9 +36,9 @@ interface DOMParser {
   [NewObject, Throws, ChromeOnly]
   Document parseFromStream(InputStream stream, DOMString? charset,
                            long contentLength, SupportedType type);
-  [Throws, ChromeOnly]
-  void init(optional Principal? principal = null,
-            optional URI? documentURI = null,
-            optional URI? baseURI = null);
+  // Can be used to allow a DOMParser to parse XUL/XBL no matter what
+  // principal it's using for the document.
+  [ChromeOnly]
+  void forceEnableXULXBL();
 };
 
diff --git a/toolkit/modules/tests/modules/MockDocument.jsm b/toolkit/modules/tests/modules/MockDocument.jsm
index 37260a2c29fb..501ba545f286 100644
--- a/toolkit/modules/tests/modules/MockDocument.jsm
+++ b/toolkit/modules/tests/modules/MockDocument.jsm
@@ -18,7 +18,6 @@ const MockDocument = {
   createTestDocument(aDocumentURL, aContent = "<form>", aType = "text/html") {
     let parser = Cc["@mozilla.org/xmlextras/domparser;1"].
                  createInstance(Ci.nsIDOMParser);
-    parser.init();
     let parsedDoc = parser.parseFromString(aContent, aType);
 
     // Assign ownerGlobal to documentElement as well for the form-less