diff --git a/dom/base/Element.cpp b/dom/base/Element.cpp
index ec6d430dc365..e56b5db3ff22 100644
--- a/dom/base/Element.cpp
+++ b/dom/base/Element.cpp
@@ -1258,7 +1258,7 @@ Element::GetAttributeNS(const nsAString& aNamespaceURI,
                         nsAString& aReturn)
 {
   int32_t nsid =
-    nsContentUtils::NameSpaceManager()->GetNameSpaceID(aNamespaceURI, OwnerDoc());
+    nsContentUtils::NameSpaceManager()->GetNameSpaceID(aNamespaceURI);
 
   if (nsid == kNameSpaceID_Unknown) {
     // Unknown namespace means no attribute.
@@ -1300,7 +1300,7 @@ Element::RemoveAttributeNS(const nsAString& aNamespaceURI,
 {
   nsCOMPtr<nsIAtom> name = NS_Atomize(aLocalName);
   int32_t nsid =
-    nsContentUtils::NameSpaceManager()->GetNameSpaceID(aNamespaceURI, OwnerDoc());
+    nsContentUtils::NameSpaceManager()->GetNameSpaceID(aNamespaceURI);
 
   if (nsid == kNameSpaceID_Unknown) {
     // If the namespace ID is unknown, it means there can't possibly be an
@@ -1377,7 +1377,7 @@ Element::HasAttributeNS(const nsAString& aNamespaceURI,
                         const nsAString& aLocalName) const
 {
   int32_t nsid =
-    nsContentUtils::NameSpaceManager()->GetNameSpaceID(aNamespaceURI, OwnerDoc());
+    nsContentUtils::NameSpaceManager()->GetNameSpaceID(aNamespaceURI);
 
   if (nsid == kNameSpaceID_Unknown) {
     // Unknown namespace means no attr...
diff --git a/dom/base/NameSpaceConstants.h b/dom/base/NameSpaceConstants.h
index d6c3f079fc47..e4cad72a4e3c 100644
--- a/dom/base/NameSpaceConstants.h
+++ b/dom/base/NameSpaceConstants.h
@@ -23,7 +23,6 @@ static const int32_t kNameSpaceID_None = 0;
 #define kNameSpaceID_RDF      8
 #define kNameSpaceID_XUL      9
 #define kNameSpaceID_SVG      10
-#define kNameSpaceID_disabled_MathML      11
-#define kNameSpaceID_LastBuiltin          11 // last 'built-in' namespace
+#define kNameSpaceID_LastBuiltin          10 // last 'built-in' namespace
 
 #endif // mozilla_dom_NameSpaceConstants_h__
diff --git a/dom/base/NodeInfo.cpp b/dom/base/NodeInfo.cpp
index 856d06c35aaf..791d4881ab2e 100644
--- a/dom/base/NodeInfo.cpp
+++ b/dom/base/NodeInfo.cpp
@@ -197,8 +197,7 @@ bool
 NodeInfo::NamespaceEquals(const nsAString& aNamespaceURI) const
 {
   int32_t nsid =
-    nsContentUtils::NameSpaceManager()->GetNameSpaceID(aNamespaceURI,
-      mOwnerManager->GetDocument());
+    nsContentUtils::NameSpaceManager()->GetNameSpaceID(aNamespaceURI);
 
   return mozilla::dom::NodeInfo::NamespaceEquals(nsid);
 }
diff --git a/dom/base/nsContentUtils.cpp b/dom/base/nsContentUtils.cpp
index e0b68ebafd83..e59869009e24 100644
--- a/dom/base/nsContentUtils.cpp
+++ b/dom/base/nsContentUtils.cpp
@@ -2892,8 +2892,7 @@ nsContentUtils::SplitQName(const nsIContent* aNamespaceResolver,
                                                         nameSpace);
     NS_ENSURE_SUCCESS(rv, rv);
 
-    *aNamespace = NameSpaceManager()->GetNameSpaceID(nameSpace,
-                                                     aNamespaceResolver->OwnerDoc());
+    *aNamespace = NameSpaceManager()->GetNameSpaceID(nameSpace);
     if (*aNamespace == kNameSpaceID_Unknown)
       return NS_ERROR_FAILURE;
 
diff --git a/dom/base/nsDOMAttributeMap.cpp b/dom/base/nsDOMAttributeMap.cpp
index ca9be88cc955..fe7de268ba98 100644
--- a/dom/base/nsDOMAttributeMap.cpp
+++ b/dom/base/nsDOMAttributeMap.cpp
@@ -446,8 +446,7 @@ nsDOMAttributeMap::GetAttrNodeInfo(const nsAString& aNamespaceURI,
 
   if (!aNamespaceURI.IsEmpty()) {
     nameSpaceID =
-      nsContentUtils::NameSpaceManager()->GetNameSpaceID(aNamespaceURI,
-                                                         mContent->OwnerDoc());
+      nsContentUtils::NameSpaceManager()->GetNameSpaceID(aNamespaceURI);
 
     if (nameSpaceID == kNameSpaceID_Unknown) {
       return nullptr;
diff --git a/dom/base/nsNameSpaceManager.cpp b/dom/base/nsNameSpaceManager.cpp
index f82bf02be8c1..fb37832f6dcc 100644
--- a/dom/base/nsNameSpaceManager.cpp
+++ b/dom/base/nsNameSpaceManager.cpp
@@ -15,25 +15,17 @@
 #include "mozilla/dom/NodeInfo.h"
 #include "nsCOMArray.h"
 #include "nsContentCreatorFunctions.h"
-#include "nsContentUtils.h"
 #include "nsGkAtoms.h"
-#include "nsIDocument.h"
 #include "nsString.h"
 #include "mozilla/dom/NodeInfo.h"
 #include "mozilla/ClearOnShutdown.h"
 #include "mozilla/dom/XBLChildrenElement.h"
 #include "mozilla/dom/Element.h"
-#include "mozilla/Preferences.h"
 
 using namespace mozilla;
 using namespace mozilla::dom;
 
-static const char* kPrefMathMLDisabled = "mathml.disabled";
-static const char* kObservedPrefs[] = {
-  kPrefMathMLDisabled,
-  nullptr
-};
-StaticRefPtr<nsNameSpaceManager> nsNameSpaceManager::sInstance;
+StaticAutoPtr<nsNameSpaceManager> nsNameSpaceManager::sInstance;
 
 /* static */ nsNameSpaceManager*
 nsNameSpaceManager::GetInstance() {
@@ -57,14 +49,6 @@ bool nsNameSpaceManager::Init()
   rv = AddNameSpace(dont_AddRef(uri), id); \
   NS_ENSURE_SUCCESS(rv, false)
 
-#define REGISTER_DISABLED_NAMESPACE(uri, id) \
-  rv = AddDisabledNameSpace(dont_AddRef(uri), id); \
-  NS_ENSURE_SUCCESS(rv, false)
-
-  mozilla::Preferences::AddStrongObservers(this, kObservedPrefs);
-  mMathMLDisabled = mozilla::Preferences::GetBool(kPrefMathMLDisabled);
-
-
   // Need to be ordered according to ID.
   REGISTER_NAMESPACE(nsGkAtoms::nsuri_xmlns, kNameSpaceID_XMLNS);
   REGISTER_NAMESPACE(nsGkAtoms::nsuri_xml, kNameSpaceID_XML);
@@ -76,10 +60,8 @@ bool nsNameSpaceManager::Init()
   REGISTER_NAMESPACE(nsGkAtoms::nsuri_rdf, kNameSpaceID_RDF);
   REGISTER_NAMESPACE(nsGkAtoms::nsuri_xul, kNameSpaceID_XUL);
   REGISTER_NAMESPACE(nsGkAtoms::nsuri_svg, kNameSpaceID_SVG);
-  REGISTER_DISABLED_NAMESPACE(nsGkAtoms::nsuri_mathml, kNameSpaceID_disabled_MathML);
 
 #undef REGISTER_NAMESPACE
-#undef REGISTER_DISABLED_NAMESPACE
 
   return true;
 }
@@ -128,32 +110,24 @@ nsNameSpaceManager::GetNameSpaceURI(int32_t aNameSpaceID, nsAString& aURI)
 }
 
 int32_t
-nsNameSpaceManager::GetNameSpaceID(const nsAString& aURI,
-                                   nsIDocument* aDocument)
+nsNameSpaceManager::GetNameSpaceID(const nsAString& aURI)
 {
   if (aURI.IsEmpty()) {
     return kNameSpaceID_None; // xmlns="", see bug 75700 for details
   }
 
   nsCOMPtr<nsIAtom> atom = NS_Atomize(aURI);
-  return GetNameSpaceID(atom, aDocument);
+  return GetNameSpaceID(atom);
 }
 
 int32_t
-nsNameSpaceManager::GetNameSpaceID(nsIAtom* aURI,
-                                   nsIDocument* aDocument)
+nsNameSpaceManager::GetNameSpaceID(nsIAtom* aURI)
 {
   if (aURI == nsGkAtoms::_empty) {
     return kNameSpaceID_None; // xmlns="", see bug 75700 for details
   }
 
   int32_t nameSpaceID;
-  if (mMathMLDisabled &&
-      mDisabledURIToIDTable.Get(aURI, &nameSpaceID) &&
-      !nsContentUtils::IsChromeDoc(aDocument)) {
-    NS_POSTCONDITION(nameSpaceID >= 0, "Bogus namespace ID");
-    return nameSpaceID;
-  }
   if (mURIToIDTable.Get(aURI, &nameSpaceID)) {
     NS_POSTCONDITION(nameSpaceID >= 0, "Bogus namespace ID");
     return nameSpaceID;
@@ -179,19 +153,7 @@ NS_NewElement(Element** aResult,
   }
 #endif
   if (ns == kNameSpaceID_MathML) {
-    // If the mathml.disabled pref. is true, convert all MathML nodes into
-    // disabled MathML nodes by swapping the namespace.
-    nsNameSpaceManager* nsmgr = nsNameSpaceManager::GetInstance();
-    if ((nsmgr && !nsmgr->mMathMLDisabled) ||
-        nsContentUtils::IsChromeDoc(ni->GetDocument())) {
-      return NS_NewMathMLElement(aResult, ni.forget());
-    }
-
-    RefPtr<mozilla::dom::NodeInfo> genericXMLNI =
-      ni->NodeInfoManager()->
-      GetNodeInfo(ni->NameAtom(), ni->GetPrefixAtom(),
-        kNameSpaceID_disabled_MathML, ni->NodeType(), ni->GetExtraName());
-    return NS_NewXMLElement(aResult, genericXMLNI.forget());
+    return NS_NewMathMLElement(aResult, ni.forget());
   }
   if (ns == kNameSpaceID_SVG) {
     return NS_NewSVGElement(aResult, ni.forget(), aFromParser);
@@ -233,35 +195,3 @@ nsresult nsNameSpaceManager::AddNameSpace(already_AddRefed<nsIAtom> aURI,
 
   return NS_OK;
 }
-
-nsresult
-nsNameSpaceManager::AddDisabledNameSpace(already_AddRefed<nsIAtom> aURI,
-                                         const int32_t aNameSpaceID)
-{
-  nsCOMPtr<nsIAtom> uri = aURI;
-  if (aNameSpaceID < 0) {
-    // We've wrapped...  Can't do anything else here; just bail.
-    return NS_ERROR_OUT_OF_MEMORY;
-  }
-
-  NS_ASSERTION(aNameSpaceID - 1 == (int32_t) mURIArray.Length(),
-               "BAD! AddDisabledNameSpace not called in right order!");
-
-  mURIArray.AppendElement(uri.forget());
-  mDisabledURIToIDTable.Put(mURIArray.LastElement(), aNameSpaceID);
-
-  return NS_OK;
-}
-
-// nsISupports
-NS_IMPL_ISUPPORTS(nsNameSpaceManager,
-                  nsIObserver)
-
-// nsIObserver
-NS_IMETHODIMP
-nsNameSpaceManager::Observe(nsISupports* aObject, const char* aTopic,
-                            const char16_t* aMessage)
-{
-  mMathMLDisabled = mozilla::Preferences::GetBool(kPrefMathMLDisabled);
-  return NS_OK;
-}
diff --git a/dom/base/nsNameSpaceManager.h b/dom/base/nsNameSpaceManager.h
index 9bbf4e6590b1..2d12391c9f31 100644
--- a/dom/base/nsNameSpaceManager.h
+++ b/dom/base/nsNameSpaceManager.h
@@ -10,8 +10,6 @@
 #include "nsDataHashtable.h"
 #include "nsHashKeys.h"
 #include "nsIAtom.h"
-#include "nsIDocument.h"
-#include "nsIObserver.h"
 #include "nsTArray.h"
 
 #include "mozilla/StaticPtr.h"
@@ -32,42 +30,34 @@ class nsAString;
  *
  */
 
-class nsNameSpaceManager final : public nsIObserver
+class nsNameSpaceManager final
 {
 public:
-  NS_DECL_ISUPPORTS
-  NS_DECL_NSIOBSERVER
-  virtual nsresult RegisterNameSpace(const nsAString& aURI,
-                                     int32_t& aNameSpaceID);
+  ~nsNameSpaceManager() {}
 
-  virtual nsresult GetNameSpaceURI(int32_t aNameSpaceID, nsAString& aURI);
+  nsresult RegisterNameSpace(const nsAString& aURI, int32_t& aNameSpaceID);
+
+  nsresult GetNameSpaceURI(int32_t aNameSpaceID, nsAString& aURI);
 
   nsIAtom* NameSpaceURIAtom(int32_t aNameSpaceID) {
     MOZ_ASSERT(aNameSpaceID > 0 && (int64_t) aNameSpaceID <= (int64_t) mURIArray.Length());
     return mURIArray.ElementAt(aNameSpaceID - 1); // id is index + 1
   }
 
-  int32_t GetNameSpaceID(const nsAString& aURI,
-                         nsIDocument* aDocument);
-  int32_t GetNameSpaceID(nsIAtom* aURI,
-                         nsIDocument* aDocument);
+  int32_t GetNameSpaceID(const nsAString& aURI);
+  int32_t GetNameSpaceID(nsIAtom* aURI);
 
   bool HasElementCreator(int32_t aNameSpaceID);
 
   static nsNameSpaceManager* GetInstance();
-  bool mMathMLDisabled;
-
 private:
   bool Init();
   nsresult AddNameSpace(already_AddRefed<nsIAtom> aURI, const int32_t aNameSpaceID);
-  nsresult AddDisabledNameSpace(already_AddRefed<nsIAtom> aURI, const int32_t aNameSpaceID);
-  ~nsNameSpaceManager() {};
 
   nsDataHashtable<nsISupportsHashKey, int32_t> mURIToIDTable;
-  nsDataHashtable<nsISupportsHashKey, int32_t> mDisabledURIToIDTable;
   nsTArray<nsCOMPtr<nsIAtom>> mURIArray;
 
-  static mozilla::StaticRefPtr<nsNameSpaceManager> sInstance;
+  static mozilla::StaticAutoPtr<nsNameSpaceManager> sInstance;
 };
  
 #endif // nsNameSpaceManager_h___
diff --git a/dom/svg/SVGAnimationElement.cpp b/dom/svg/SVGAnimationElement.cpp
index c9d1191daf4b..9b8431c7e4fe 100644
--- a/dom/svg/SVGAnimationElement.cpp
+++ b/dom/svg/SVGAnimationElement.cpp
@@ -348,15 +348,6 @@ SVGAnimationElement::IsNodeOfType(uint32_t aFlags) const
   return !(aFlags & ~(eCONTENT | eANIMATION));
 }
 
-//----------------------------------------------------------------------
-// SVGTests methods
-
-bool
-SVGAnimationElement::IsInChromeDoc() const
-{
-  return nsContentUtils::IsChromeDoc(OwnerDoc());
-}
-
 //----------------------------------------------------------------------
 // SVG utility methods
 
diff --git a/dom/svg/SVGAnimationElement.h b/dom/svg/SVGAnimationElement.h
index 9bcbdf0c2214..8297a339fb97 100644
--- a/dom/svg/SVGAnimationElement.h
+++ b/dom/svg/SVGAnimationElement.h
@@ -86,10 +86,6 @@ public:
   void EndElement(ErrorResult& rv) { EndElementAt(0.f, rv); }
   void EndElementAt(float offset, ErrorResult& rv);
 
-  // SVGTests
-  virtual bool IsInChromeDoc() const override;
-
-
  protected:
   // nsSVGElement overrides
 
diff --git a/dom/svg/SVGGraphicsElement.cpp b/dom/svg/SVGGraphicsElement.cpp
index ba6306680317..d4e0fe50b37c 100644
--- a/dom/svg/SVGGraphicsElement.cpp
+++ b/dom/svg/SVGGraphicsElement.cpp
@@ -31,11 +31,5 @@ SVGGraphicsElement::~SVGGraphicsElement()
 {
 }
 
-bool
-SVGGraphicsElement::IsInChromeDoc() const
-{
-  return nsContentUtils::IsChromeDoc(OwnerDoc());
-}
-
 } // namespace dom
 } // namespace mozilla
diff --git a/dom/svg/SVGGraphicsElement.h b/dom/svg/SVGGraphicsElement.h
index a6437dba9ed6..57a284fda1e8 100644
--- a/dom/svg/SVGGraphicsElement.h
+++ b/dom/svg/SVGGraphicsElement.h
@@ -25,8 +25,6 @@ protected:
 public:
   // interfaces:
   NS_DECL_ISUPPORTS_INHERITED
-
-  bool IsInChromeDoc() const override;
 };
 
 } // namespace dom
diff --git a/dom/svg/SVGSymbolElement.cpp b/dom/svg/SVGSymbolElement.cpp
index 42de96efd182..7f77b464edb2 100644
--- a/dom/svg/SVGSymbolElement.cpp
+++ b/dom/svg/SVGSymbolElement.cpp
@@ -80,16 +80,6 @@ SVGSymbolElement::IsAttributeMapped(const nsIAtom* name) const
     SVGSymbolElementBase::IsAttributeMapped(name);
 }
 
-//----------------------------------------------------------------------
-// SVGTests methods
-
-bool
-SVGSymbolElement::IsInChromeDoc() const
-{
-  return nsContentUtils::IsChromeDoc(OwnerDoc());
-}
-
-
 //----------------------------------------------------------------------
 // nsSVGElement methods
 
diff --git a/dom/svg/SVGSymbolElement.h b/dom/svg/SVGSymbolElement.h
index 427840f3f2fe..dd28a2da717a 100644
--- a/dom/svg/SVGSymbolElement.h
+++ b/dom/svg/SVGSymbolElement.h
@@ -44,9 +44,6 @@ public:
   already_AddRefed<SVGAnimatedRect> ViewBox();
   already_AddRefed<DOMSVGAnimatedPreserveAspectRatio> PreserveAspectRatio();
 
-  // SVGTests
-  bool IsInChromeDoc() const override;
-
 protected:
   virtual nsSVGViewBox *GetViewBox() override;
   virtual SVGAnimatedPreserveAspectRatio *GetPreserveAspectRatio() override;
diff --git a/dom/svg/SVGTests.cpp b/dom/svg/SVGTests.cpp
index 0fa83ca9f7b0..ab8077dd5aef 100644
--- a/dom/svg/SVGTests.cpp
+++ b/dom/svg/SVGTests.cpp
@@ -57,7 +57,7 @@ SVGTests::SystemLanguage()
 bool
 SVGTests::HasExtension(const nsAString& aExtension)
 {
-  return nsSVGFeatures::HasExtension(aExtension, IsInChromeDoc());
+  return nsSVGFeatures::HasExtension(aExtension);
 }
 
 bool
@@ -139,7 +139,7 @@ SVGTests::PassesConditionalProcessingTests(const nsString *aAcceptLangs) const
       return false;
     }
     for (uint32_t i = 0; i < mStringListAttributes[EXTENSIONS].Length(); i++) {
-      if (!nsSVGFeatures::HasExtension(mStringListAttributes[EXTENSIONS][i], IsInChromeDoc())) {
+      if (!nsSVGFeatures::HasExtension(mStringListAttributes[EXTENSIONS][i])) {
         return false;
       }
     }
diff --git a/dom/svg/SVGTests.h b/dom/svg/SVGTests.h
index 1e0de76e3f09..4e65e5b9d13a 100644
--- a/dom/svg/SVGTests.h
+++ b/dom/svg/SVGTests.h
@@ -95,8 +95,6 @@ public:
   already_AddRefed<DOMSVGStringList> SystemLanguage();
   bool HasExtension(const nsAString& aExtension);
 
-  virtual bool IsInChromeDoc() const = 0;
-
 protected:
   virtual ~SVGTests() {}
 
diff --git a/dom/svg/nsSVGFeatures.cpp b/dom/svg/nsSVGFeatures.cpp
index 1b028250b6d3..3ce6d3697e31 100644
--- a/dom/svg/nsSVGFeatures.cpp
+++ b/dom/svg/nsSVGFeatures.cpp
@@ -15,7 +15,6 @@
 #include "nsSVGFeatures.h"
 #include "nsIContent.h"
 #include "nsIDocument.h"
-#include "nsNameSpaceManager.h"
 #include "mozilla/Preferences.h"
 
 using namespace mozilla;
@@ -43,14 +42,11 @@ nsSVGFeatures::HasFeature(nsISupports* aObject, const nsAString& aFeature)
 }
 
 /*static*/ bool
-nsSVGFeatures::HasExtension(const nsAString& aExtension, const bool aIsInChrome)
+nsSVGFeatures::HasExtension(const nsAString& aExtension)
 {
 #define SVG_SUPPORTED_EXTENSION(str) if (aExtension.EqualsLiteral(str)) return true;
   SVG_SUPPORTED_EXTENSION("http://www.w3.org/1999/xhtml")
-  nsNameSpaceManager* nameSpaceManager = nsNameSpaceManager::GetInstance();
-  if (aIsInChrome || !nameSpaceManager->mMathMLDisabled) {
-    SVG_SUPPORTED_EXTENSION("http://www.w3.org/1998/Math/MathML")
-  }
+  SVG_SUPPORTED_EXTENSION("http://www.w3.org/1998/Math/MathML")
 #undef SVG_SUPPORTED_EXTENSION
 
   return false;
diff --git a/dom/svg/nsSVGFeatures.h b/dom/svg/nsSVGFeatures.h
index 0e8ad3eec1a6..248f36a99f10 100644
--- a/dom/svg/nsSVGFeatures.h
+++ b/dom/svg/nsSVGFeatures.h
@@ -30,7 +30,7 @@ public:
    *   "http://www.w3.org/1999/xhtml" and "http://www.w3.org/1998/Math/MathML"
    */
   static bool
-  HasExtension(const nsAString& aExtension, const bool aIsInChrome);
+  HasExtension(const nsAString& aExtension);
 };
 
 #endif // __NS_SVGFEATURES_H__
diff --git a/dom/xbl/nsXBLPrototypeBinding.cpp b/dom/xbl/nsXBLPrototypeBinding.cpp
index 43ad448c405d..5152360f82af 100644
--- a/dom/xbl/nsXBLPrototypeBinding.cpp
+++ b/dom/xbl/nsXBLPrototypeBinding.cpp
@@ -1599,7 +1599,7 @@ nsXBLPrototypeBinding::ResolveBaseBinding()
     mBinding->LookupNamespaceURI(prefix, nameSpace);
     if (!nameSpace.IsEmpty()) {
       int32_t nameSpaceID =
-        nsContentUtils::NameSpaceManager()->GetNameSpaceID(nameSpace, doc);
+        nsContentUtils::NameSpaceManager()->GetNameSpaceID(nameSpace);
 
       nsCOMPtr<nsIAtom> tagName = NS_Atomize(display);
       // Check the white list
diff --git a/dom/xml/nsXMLContentSink.cpp b/dom/xml/nsXMLContentSink.cpp
index aeaa302f466c..d36c1fb1b4f2 100644
--- a/dom/xml/nsXMLContentSink.cpp
+++ b/dom/xml/nsXMLContentSink.cpp
@@ -1049,9 +1049,6 @@ nsXMLContentSink::HandleEndElement(const char16_t *aName,
   bool isTemplateElement = debugTagAtom == nsGkAtoms::_template &&
                            debugNameSpaceID == kNameSpaceID_XHTML;
   NS_ASSERTION(content->NodeInfo()->Equals(debugTagAtom, debugNameSpaceID) ||
-               (debugNameSpaceID == kNameSpaceID_MathML &&
-                content->NodeInfo()->NamespaceID() == kNameSpaceID_disabled_MathML &&
-                content->NodeInfo()->Equals(debugTagAtom)) ||
                isTemplateElement, "Wrong element being closed");
 #endif
 
diff --git a/layout/mathml/moz.build b/layout/mathml/moz.build
index f40b2c2c6589..c177c552b467 100644
--- a/layout/mathml/moz.build
+++ b/layout/mathml/moz.build
@@ -12,9 +12,6 @@ if CONFIG['ENABLE_TESTS']:
         'imptests/mochitest.ini',
         'tests/mochitest.ini',
 ]
-    MOCHITEST_CHROME_MANIFESTS += [
-        'tests/chrome.ini',
-]
 
 UNIFIED_SOURCES += [
     'nsMathMLChar.cpp',
diff --git a/layout/mathml/tests/chrome.ini b/layout/mathml/tests/chrome.ini
deleted file mode 100644
index 0885f4c6b378..000000000000
--- a/layout/mathml/tests/chrome.ini
+++ /dev/null
@@ -1,6 +0,0 @@
-[DEFAULT]
-
-support-files =
-  mathml_example_test.html
-
-[test_disabled_chrome.html]
diff --git a/layout/mathml/tests/mathml_example_test.html b/layout/mathml/tests/mathml_example_test.html
deleted file mode 100644
index 6eee75d01384..000000000000
--- a/layout/mathml/tests/mathml_example_test.html
+++ /dev/null
@@ -1,28 +0,0 @@
-<math xmlns="http://www.w3.org/1998/Math/MathML">
-  <mstyle scriptsizemultiplier="2">
-    <msub>
-      <mtext>O</mtext>
-      <mtext>O</mtext>
-    </msub>
-    <msup>
-      <mtext>O</mtext>
-      <mtext>O</mtext>
-    </msup>
-    <msubsup>
-      <mtext>O</mtext>
-      <mtext>O</mtext>
-      <mtext>O</mtext>
-    </msubsup>
-    <mmultiscripts>
-      <mtext>O</mtext>
-      <mtext>O</mtext>
-      <mtext>O</mtext>
-      <mprescripts/>
-      <mtext>O</mtext>
-      <mtext>O</mtext>
-    </mmultiscripts>
-  </mstyle>
-</math>
-
-<svg id="svgel">
-</svg>
diff --git a/layout/mathml/tests/mochitest.ini b/layout/mathml/tests/mochitest.ini
index 6a665150964b..3d7960c72c95 100644
--- a/layout/mathml/tests/mochitest.ini
+++ b/layout/mathml/tests/mochitest.ini
@@ -6,7 +6,6 @@
 [test_bug827713-2.html]
 [test_bug827713.html]
 [test_bug975681.html]
-[test_disabled.html]
 [test_opentype-axis-height.html]
 [test_opentype-fraction.html]
 [test_opentype-limits.html]
diff --git a/layout/mathml/tests/test_disabled.html b/layout/mathml/tests/test_disabled.html
deleted file mode 100644
index 9b649d0f9c45..000000000000
--- a/layout/mathml/tests/test_disabled.html
+++ /dev/null
@@ -1,47 +0,0 @@
-<!DOCTYPE HTML>
-<html>
-<!--
-Copied from
-https://bugzilla.mozilla.org/show_bug.cgi?id=744830
--->
-<head>
-  <script type="application/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
-  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
-</head>
-<body>
-<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=166235">Mozilla Bug 166235</a>
-<div id="testnodes"><span>hi</span> there <!-- mon ami --></div>
-<pre id="test">
-<script type="application/javascript">
-  SimpleTest.waitForExplicitFinish();
-  SpecialPowers.pushPrefEnv({"set": [["mathml.disabled", true]]}, doTest);
-  function doTest() {
-    let t = document.getElementById('testnodes');
-    t.innerHTML = null;
-    t.appendChild(document.createElementNS("http://www.w3.org/1998/Math/MathML", "math:math"));
-    t.firstChild.textContent = "<foo>";
-    is(t.innerHTML, "<math:math>&lt;foo&gt;</math:math>");
-
-    t.innerHTML = null;
-    t.appendChild(document.createElementNS("http://www.w3.org/1998/Math/MathML", "math"));
-    is(t.firstChild.namespaceURI, "http://www.w3.org/1998/Math/MathML");
-    t.firstChild.appendChild(document.createElementNS("http://www.w3.org/1998/Math/MathML", "script"));
-    is(t.firstChild.firstChild.namespaceURI, "http://www.w3.org/1998/Math/MathML");
-    t.firstChild.firstChild.textContent = "1&2<3>4\xA0";
-    is(t.innerHTML, '<math><script>1&amp;2&lt;3&gt;4&nbsp;\u003C/script></math>');
-
-    t.innerHTML = null;
-    t.appendChild(document.createElementNS("http://www.w3.org/1998/Math/MathML", "math"));
-    is(t.firstChild.namespaceURI, "http://www.w3.org/1998/Math/MathML");
-    t.firstChild.appendChild(document.createElementNS("http://www.w3.org/1998/Math/MathML", "style"));
-    is(t.firstChild.firstChild.namespaceURI, "http://www.w3.org/1998/Math/MathML");
-    t.firstChild.firstChild.textContent = "1&2<3>4\xA0";
-    is(t.innerHTML, '<math><style>1&amp;2&lt;3&gt;4&nbsp;\u003C/style></math>');
-
-    SimpleTest.finish();
-  }
-</script>
-</pre>
-</body>
-</html>
-
diff --git a/layout/mathml/tests/test_disabled_chrome.html b/layout/mathml/tests/test_disabled_chrome.html
deleted file mode 100644
index dff4011bb776..000000000000
--- a/layout/mathml/tests/test_disabled_chrome.html
+++ /dev/null
@@ -1,55 +0,0 @@
-<!DOCTYPE HTML>
-<html>
-<!--
-https://bugzilla.mozilla.org/show_bug.cgi?id=744830
--->
-<head>
-  <script type="application/javascript" src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"></script>
-<!--
-  <script type="application/javascript" src="chrome://mochikit/content/tests/SimpleTest/EventUtils.js"></script>
--->
-  <script type="application/javascript" src="chrome://mochikit/content/tests/SimpleTest/SpawnTask.js"></script>
-  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
-</head>
-<body>
-<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=166235">Mozilla Bug 166235</a>
-<div id="testnodes"><span>hi</span> there <!-- mon ami --></div>
-<pre id="test">
-<script type="application/javascript">
-  add_task(function* () {
-    const initialPrefValue = SpecialPowers.getBoolPref("mathml.disabled");
-    SpecialPowers.setBoolPref("mathml.disabled", true);
-    const Cu = SpecialPowers.Components.utils;
-    const { ContentTaskUtils } = Cu.import("resource://testing-common/ContentTaskUtils.jsm", {});
-    let t = document.getElementById('testnodes');
-
-    let url = 'chrome://mochitests/content/chrome/layout/mathml/tests/mathml_example_test.html'
-    const chromeIframeEl = document.createElement('iframe');
-    let chromeLoadPromise = ContentTaskUtils.waitForEvent(chromeIframeEl, 'load', false);
-    chromeIframeEl.src = url;
-    t.appendChild(chromeIframeEl);
-
-    yield chromeLoadPromise;
-    const chromeBR = chromeIframeEl.contentDocument.body.getBoundingClientRect();
-
-    url = "http://mochi.test:8888/chrome/layout/mathml/tests/mathml_example_test.html";
-    const iframeEl = document.createElement('iframe');
-    iframeEl.src = url;
-    let loadPromise = ContentTaskUtils.waitForEvent(iframeEl, 'load', false);
-    t.appendChild(iframeEl);
-    yield loadPromise;
-
-    const contentBR = iframeEl.contentDocument.body.getBoundingClientRect();
-
-    ok(chromeBR.height > contentBR.height, "Chrome content height should be bigger than content due to layout");
-
-    ok(!iframeEl.contentDocument.getElementById('svgel').hasExtension("http://www.w3.org/1998/Math/MathML"), 'SVG namespace support is disabled in content iframe');
-    ok(chromeIframeEl.contentDocument.getElementById('svgel').hasExtension("http://www.w3.org/1998/Math/MathML"), 'SVG namespace support is enabled in chrome iframe');
-
-    SpecialPowers.setBoolPref("mathml.disabled", initialPrefValue);
-  });
-</script>
-</pre>
-</body>
-</html>
-
diff --git a/layout/reftests/mathml/disabled-scriptlevel-1-ref.html b/layout/reftests/mathml/disabled-scriptlevel-1-ref.html
deleted file mode 100644
index 76658a0b678d..000000000000
--- a/layout/reftests/mathml/disabled-scriptlevel-1-ref.html
+++ /dev/null
@@ -1,129 +0,0 @@
-<!DOCTYPE html>
-<html>
-  <head>
-    <title>scriptlevel</title>
-    <meta charset="utf-8"/>
-  </head>
-  <body>
-
-    <!-- Test scriptlevel on mstyle -->
-    <randomelement>
-      <mstyle scriptsizemultiplier="2">
-        <mtext>O</mtext>
-        <mstyle scriptlevel="1"><mtext>O</mtext></mstyle>
-      </mstyle>
-    </randomelement>
-
-    <!-- The mfrac element sets displaystyle to "false", or if it was already
-         false increments scriptlevel by 1, within numerator and denominator.
-      -->
-    <randomelement>
-      <mstyle scriptsizemultiplier="2">
-        <mstyle displaystyle="false">
-          <mfrac>
-            <mtext>O</mtext>
-            <mtext>O</mtext>
-          </mfrac>
-        </mstyle>
-        <mstyle displaystyle="true">
-          <mfrac>
-            <mtext>O</mtext>
-            <mtext>O</mtext>
-          </mfrac>
-        </mstyle>
-      </mstyle>
-    </randomelement>
-
-    <!--    The mroot element increments scriptlevel by 2, and sets
-            displaystyle to "false", within index, but leaves both attributes
-            unchanged within base.
-            The msqrt element leaves both attributes unchanged within its
-            argument. -->
-    <randomelement>
-      <mstyle scriptsizemultiplier="2">
-        <mroot>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-        </mroot>
-        <msqrt>
-          <mtext>O</mtext>
-        </msqrt>
-      </mstyle>
-    </randomelement>
-
-<!--
-    The msub element [...] increments scriptlevel by 1, and sets displaystyle to
-   "false", within subscript, but leaves both attributes unchanged within base.
-
-   The msup element [...] increments scriptlevel by 1, and sets displaystyle to
-   "false", within superscript, but leaves both attributes unchanged within
-   base.
-
-   The msubsup element [...] increments scriptlevel by 1, and sets displaystyle
-   to "false", within subscript and superscript, but leaves both attributes
-   unchanged within base.
-
-   The mmultiscripts element increments scriptlevel by 1, and sets displaystyle
-   to "false", within each of its arguments except base, but leaves both
-   attributes unchanged within base.
-   -->
-    <randomelement>
-      <mstyle scriptsizemultiplier="2">
-        <msub>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-        </msub>
-        <msup>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-        </msup>
-        <msubsup>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-        </msubsup>
-        <mmultiscripts>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-          <mprescripts/>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-        </mmultiscripts>
-      </mstyle>
-    </randomelement>
-
-<!-- 
-   The munder element [...] always sets displaystyle to "false" within the
-   underscript, but increments scriptlevel by 1 only when accentunder is
-   "false". Within base, it always leaves both attributes unchanged.
-
-   The mover element [...] always sets displaystyle to "false" within
-   overscript, but increments scriptlevel by 1 only when accent is "false".
-   Within base, it always leaves both attributes unchanged.
-
-   The munderover [..] always sets displaystyle to "false" within underscript
-   and overscript, but increments scriptlevel by 1 only when accentunder or
-   accent, respectively, are "false". Within base, it always leaves both
-   attributes unchanged.
--->   
-    <randomelement>
-      <mstyle scriptsizemultiplier="2">
-        <munder>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-        </munder>
-        <mover>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-        </mover>
-        <munderover>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-        </munderover>
-      </mstyle>
-    </randomelement>
-
-  </body>
-</html>
diff --git a/layout/reftests/mathml/disabled-scriptlevel-1-ref.xhtml b/layout/reftests/mathml/disabled-scriptlevel-1-ref.xhtml
deleted file mode 100644
index 6b22791ab83f..000000000000
--- a/layout/reftests/mathml/disabled-scriptlevel-1-ref.xhtml
+++ /dev/null
@@ -1,133 +0,0 @@
-<html xmlns="http://www.w3.org/1999/xhtml">
-  <head>
-    <title>scriptlevel</title>
-    <meta charset="utf-8"/>
-    <style>
-      h2 {
-        text-align:center;
-      }
-    </style>
-  </head>
-  <body>
-
-    <!-- Test scriptlevel on mstyle -->
-    <randomelement>
-      <mstyle scriptsizemultiplier="2">
-        <mtext>O</mtext>
-        <mstyle scriptlevel="1"><mtext>O</mtext></mstyle>
-      </mstyle>
-    </randomelement>
-
-    <!-- The mfrac element sets displaystyle to "false", or if it was already
-         false increments scriptlevel by 1, within numerator and denominator.
-      -->
-    <randomelement>
-      <mstyle scriptsizemultiplier="2">
-        <mstyle displaystyle="false">
-          <mfrac>
-            <mtext>O</mtext>
-            <mtext>O</mtext>
-          </mfrac>
-        </mstyle>
-        <mstyle displaystyle="true">
-          <mfrac>
-            <mtext>O</mtext>
-            <mtext>O</mtext>
-          </mfrac>
-        </mstyle>
-      </mstyle>
-    </randomelement>
-
-    <!--    The mroot element increments scriptlevel by 2, and sets
-            displaystyle to "false", within index, but leaves both attributes
-            unchanged within base.
-            The msqrt element leaves both attributes unchanged within its
-            argument. -->
-    <randomelement>
-      <mstyle scriptsizemultiplier="2">
-        <mroot>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-        </mroot>
-        <msqrt>
-          <mtext>O</mtext>
-        </msqrt>
-      </mstyle>
-    </randomelement>
-
-<!--
-    The msub element [...] increments scriptlevel by 1, and sets displaystyle to
-   "false", within subscript, but leaves both attributes unchanged within base.
-
-   The msup element [...] increments scriptlevel by 1, and sets displaystyle to
-   "false", within superscript, but leaves both attributes unchanged within
-   base.
-
-   The msubsup element [...] increments scriptlevel by 1, and sets displaystyle
-   to "false", within subscript and superscript, but leaves both attributes
-   unchanged within base.
-
-   The mmultiscripts element increments scriptlevel by 1, and sets displaystyle
-   to "false", within each of its arguments except base, but leaves both
-   attributes unchanged within base.
-   -->
-    <randomelement>
-      <mstyle scriptsizemultiplier="2">
-        <msub>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-        </msub>
-        <msup>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-        </msup>
-        <msubsup>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-        </msubsup>
-        <mmultiscripts>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-          <mprescripts/>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-        </mmultiscripts>
-      </mstyle>
-    </randomelement>
-
-<!-- 
-   The munder element [...] always sets displaystyle to "false" within the
-   underscript, but increments scriptlevel by 1 only when accentunder is
-   "false". Within base, it always leaves both attributes unchanged.
-
-   The mover element [...] always sets displaystyle to "false" within
-   overscript, but increments scriptlevel by 1 only when accent is "false".
-   Within base, it always leaves both attributes unchanged.
-
-   The munderover [..] always sets displaystyle to "false" within underscript
-   and overscript, but increments scriptlevel by 1 only when accentunder or
-   accent, respectively, are "false". Within base, it always leaves both
-   attributes unchanged.
--->   
-    <randomelement>
-      <mstyle scriptsizemultiplier="2">
-        <munder>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-        </munder>
-        <mover>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-        </mover>
-        <munderover>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-        </munderover>
-      </mstyle>
-    </randomelement>
-
-  </body>
-</html>
diff --git a/layout/reftests/mathml/disabled-scriptlevel-1.html b/layout/reftests/mathml/disabled-scriptlevel-1.html
deleted file mode 100644
index 9cd388f1c77c..000000000000
--- a/layout/reftests/mathml/disabled-scriptlevel-1.html
+++ /dev/null
@@ -1,129 +0,0 @@
-<!DOCTYPE html>
-<html>
-  <head>
-    <title>scriptlevel</title>
-    <meta charset="utf-8"/>
-  </head>
-  <body>
-
-    <!-- Test scriptlevel on mstyle -->
-    <math>
-      <mstyle scriptsizemultiplier="2">
-        <mtext>O</mtext>
-        <mstyle scriptlevel="1"><mtext>O</mtext></mstyle>
-      </mstyle>
-    </math>
-
-    <!-- The mfrac element sets displaystyle to "false", or if it was already
-         false increments scriptlevel by 1, within numerator and denominator.
-      -->
-    <math>
-      <mstyle scriptsizemultiplier="2">
-        <mstyle displaystyle="false">
-          <mfrac>
-            <mtext>O</mtext>
-            <mtext>O</mtext>
-          </mfrac>
-        </mstyle>
-        <mstyle displaystyle="true">
-          <mfrac>
-            <mtext>O</mtext>
-            <mtext>O</mtext>
-          </mfrac>
-        </mstyle>
-      </mstyle>
-    </math>
-
-    <!--    The mroot element increments scriptlevel by 2, and sets
-            displaystyle to "false", within index, but leaves both attributes
-            unchanged within base.
-            The msqrt element leaves both attributes unchanged within its
-            argument. -->
-    <math>
-      <mstyle scriptsizemultiplier="2">
-        <mroot>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-        </mroot>
-        <msqrt>
-          <mtext>O</mtext>
-        </msqrt>
-      </mstyle>
-    </math>
-
-<!--
-    The msub element [...] increments scriptlevel by 1, and sets displaystyle to
-   "false", within subscript, but leaves both attributes unchanged within base.
-
-   The msup element [...] increments scriptlevel by 1, and sets displaystyle to
-   "false", within superscript, but leaves both attributes unchanged within
-   base.
-
-   The msubsup element [...] increments scriptlevel by 1, and sets displaystyle
-   to "false", within subscript and superscript, but leaves both attributes
-   unchanged within base.
-
-   The mmultiscripts element increments scriptlevel by 1, and sets displaystyle
-   to "false", within each of its arguments except base, but leaves both
-   attributes unchanged within base.
-   -->
-    <math>
-      <mstyle scriptsizemultiplier="2">
-        <msub>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-        </msub>
-        <msup>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-        </msup>
-        <msubsup>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-        </msubsup>
-        <mmultiscripts>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-          <mprescripts/>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-        </mmultiscripts>
-      </mstyle>
-    </math>
-
-<!-- 
-   The munder element [...] always sets displaystyle to "false" within the
-   underscript, but increments scriptlevel by 1 only when accentunder is
-   "false". Within base, it always leaves both attributes unchanged.
-
-   The mover element [...] always sets displaystyle to "false" within
-   overscript, but increments scriptlevel by 1 only when accent is "false".
-   Within base, it always leaves both attributes unchanged.
-
-   The munderover [..] always sets displaystyle to "false" within underscript
-   and overscript, but increments scriptlevel by 1 only when accentunder or
-   accent, respectively, are "false". Within base, it always leaves both
-   attributes unchanged.
--->   
-    <math>
-      <mstyle scriptsizemultiplier="2">
-        <munder>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-        </munder>
-        <mover>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-        </mover>
-        <munderover>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-        </munderover>
-      </mstyle>
-    </math>
-
-  </body>
-</html>
diff --git a/layout/reftests/mathml/disabled-scriptlevel-1.xhtml b/layout/reftests/mathml/disabled-scriptlevel-1.xhtml
deleted file mode 100644
index 5d710a787c2c..000000000000
--- a/layout/reftests/mathml/disabled-scriptlevel-1.xhtml
+++ /dev/null
@@ -1,133 +0,0 @@
-<html xmlns="http://www.w3.org/1999/xhtml">
-  <head>
-    <title>scriptlevel</title>
-    <meta charset="utf-8"/>
-    <style>
-      h2 {
-        text-align:center;
-      }
-    </style>
-  </head>
-  <body>
-
-    <!-- Test scriptlevel on mstyle -->
-    <math xmlns="http://www.w3.org/1998/Math/MathML">
-      <mstyle scriptsizemultiplier="2">
-        <mtext>O</mtext>
-        <mstyle scriptlevel="1"><mtext>O</mtext></mstyle>
-      </mstyle>
-    </math>
-
-    <!-- The mfrac element sets displaystyle to "false", or if it was already
-         false increments scriptlevel by 1, within numerator and denominator.
-      -->
-    <math xmlns="http://www.w3.org/1998/Math/MathML">
-      <mstyle scriptsizemultiplier="2">
-        <mstyle displaystyle="false">
-          <mfrac>
-            <mtext>O</mtext>
-            <mtext>O</mtext>
-          </mfrac>
-        </mstyle>
-        <mstyle displaystyle="true">
-          <mfrac>
-            <mtext>O</mtext>
-            <mtext>O</mtext>
-          </mfrac>
-        </mstyle>
-      </mstyle>
-    </math>
-
-    <!--    The mroot element increments scriptlevel by 2, and sets
-            displaystyle to "false", within index, but leaves both attributes
-            unchanged within base.
-            The msqrt element leaves both attributes unchanged within its
-            argument. -->
-    <math xmlns="http://www.w3.org/1998/Math/MathML">
-      <mstyle scriptsizemultiplier="2">
-        <mroot>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-        </mroot>
-        <msqrt>
-          <mtext>O</mtext>
-        </msqrt>
-      </mstyle>
-    </math>
-
-<!--
-    The msub element [...] increments scriptlevel by 1, and sets displaystyle to
-   "false", within subscript, but leaves both attributes unchanged within base.
-
-   The msup element [...] increments scriptlevel by 1, and sets displaystyle to
-   "false", within superscript, but leaves both attributes unchanged within
-   base.
-
-   The msubsup element [...] increments scriptlevel by 1, and sets displaystyle
-   to "false", within subscript and superscript, but leaves both attributes
-   unchanged within base.
-
-   The mmultiscripts element increments scriptlevel by 1, and sets displaystyle
-   to "false", within each of its arguments except base, but leaves both
-   attributes unchanged within base.
-   -->
-    <math xmlns="http://www.w3.org/1998/Math/MathML">
-      <mstyle scriptsizemultiplier="2">
-        <msub>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-        </msub>
-        <msup>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-        </msup>
-        <msubsup>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-        </msubsup>
-        <mmultiscripts>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-          <mprescripts/>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-        </mmultiscripts>
-      </mstyle>
-    </math>
-
-<!-- 
-   The munder element [...] always sets displaystyle to "false" within the
-   underscript, but increments scriptlevel by 1 only when accentunder is
-   "false". Within base, it always leaves both attributes unchanged.
-
-   The mover element [...] always sets displaystyle to "false" within
-   overscript, but increments scriptlevel by 1 only when accent is "false".
-   Within base, it always leaves both attributes unchanged.
-
-   The munderover [..] always sets displaystyle to "false" within underscript
-   and overscript, but increments scriptlevel by 1 only when accentunder or
-   accent, respectively, are "false". Within base, it always leaves both
-   attributes unchanged.
--->   
-    <math xmlns="http://www.w3.org/1998/Math/MathML">
-      <mstyle scriptsizemultiplier="2">
-        <munder>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-        </munder>
-        <mover>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-        </mover>
-        <munderover>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-          <mtext>O</mtext>
-        </munderover>
-      </mstyle>
-    </math>
-
-  </body>
-</html>
diff --git a/layout/reftests/mathml/reftest.list b/layout/reftests/mathml/reftest.list
index 8afb1082bf89..cf0ddd9305cb 100644
--- a/layout/reftests/mathml/reftest.list
+++ b/layout/reftests/mathml/reftest.list
@@ -11,8 +11,6 @@ fails == dir-9.html dir-9-ref.html # Bug 787215
 == dir-10.html dir-10-ref.html
 random-if((B2G&&browserIsRemote)||Mulet) == dir-11.html dir-11-ref.html # Initial mulet triage: parity with B2G/B2G Desktop
 == css-spacing-1.html css-spacing-1-ref.html
-pref(mathml.disabled,true) == disabled-scriptlevel-1.html disabled-scriptlevel-1-ref.html
-pref(mathml.disabled,true) == disabled-scriptlevel-1.xhtml disabled-scriptlevel-1-ref.xhtml
 == displaystyle-1.html displaystyle-1-ref.html
 == displaystyle-2.html displaystyle-2-ref.html
 == displaystyle-3.html displaystyle-3-ref.html
diff --git a/layout/style/ServoBindings.cpp b/layout/style/ServoBindings.cpp
index f8ce49d470b2..3442e28d4547 100644
--- a/layout/style/ServoBindings.cpp
+++ b/layout/style/ServoBindings.cpp
@@ -232,8 +232,7 @@ static bool
 DoMatch(Implementor* aElement, nsIAtom* aNS, nsIAtom* aName, MatchFn aMatch)
 {
   if (aNS) {
-    int32_t ns = nsContentUtils::NameSpaceManager()->GetNameSpaceID(aNS,
-                                                                    aElement->OwnerDoc());
+    int32_t ns = nsContentUtils::NameSpaceManager()->GetNameSpaceID(aNS);
     NS_ENSURE_TRUE(ns != kNameSpaceID_Unknown, false);
     const nsAttrValue* value = aElement->GetParsedAttr(aName, ns);
     return value && aMatch(value);
diff --git a/modules/libpref/init/all.js b/modules/libpref/init/all.js
index 31351a4ee24a..dc761a4b8541 100644
--- a/modules/libpref/init/all.js
+++ b/modules/libpref/init/all.js
@@ -280,9 +280,6 @@ pref("print.shrink-to-fit.scale-limit-percent", 20);
 // Whether we should display simplify page checkbox on print preview UI
 pref("print.use_simplify_page", false);
 
-// Disable support for MathML
-pref("mathml.disabled",    false);
-
 // Enable scale transform for stretchy MathML operators. See bug 414277.
 pref("mathml.scale_stretchy_operators.enabled", true);
 
diff --git a/testing/web-platform/mozilla/meta/MANIFEST.json b/testing/web-platform/mozilla/meta/MANIFEST.json
index 221d5356697c..11cbfa0b451e 100644
--- a/testing/web-platform/mozilla/meta/MANIFEST.json
+++ b/testing/web-platform/mozilla/meta/MANIFEST.json
@@ -9,16 +9,7 @@
   "local_changes": {
     "deleted": [],
     "deleted_reftests": {},
-    "items": {
-      "testharness": {
-        "html/syntax/parsing/math-parse01.html": [
-          {
-            "path": "html/syntax/parsing/math-parse01.html",
-            "url": "/html/syntax/parsing/math-parse01.html"
-          }
-        ]
-      }
-    },
+    "items": {},
     "reftest_nodes": {}
   },
   "reftest_nodes": {},
diff --git a/testing/web-platform/mozilla/meta/html/syntax/parsing/math-parse01.html.ini b/testing/web-platform/mozilla/meta/html/syntax/parsing/math-parse01.html.ini
deleted file mode 100644
index 73bc9da25c6d..000000000000
--- a/testing/web-platform/mozilla/meta/html/syntax/parsing/math-parse01.html.ini
+++ /dev/null
@@ -1,2 +0,0 @@
-[math-parse01.html]
-  prefs: ["mathml.disabled:true"]
diff --git a/testing/web-platform/mozilla/tests/html/syntax/parsing/math-parse01.html b/testing/web-platform/mozilla/tests/html/syntax/parsing/math-parse01.html
deleted file mode 100644
index 3aff716d9f7c..000000000000
--- a/testing/web-platform/mozilla/tests/html/syntax/parsing/math-parse01.html
+++ /dev/null
@@ -1,62 +0,0 @@
-<!DOCTYPE html>
-<html>
-<head>
-<title>math in html: parsing</title>
-<script src="/resources/testharness.js"></script>
-<script src="/resources/testharnessreport.js"></script>
-</head>
-<body>
-<h1>math in html: parsing</h1>
-
-<div id="log" style="display:block"></div>
-
-<div style="display:none">
-<div><math id="m1"><mtext/></math></div>
-<div id="d1"><math><mrow/><mi/></math></div>
-<div id="d2"><math><mrow><mrow><mn>1</mn></mrow><mi>a</mi></mrow></math></div>
-<div id="d3">&lang;&rang;</div>
-<div id="d4">&Kopf;</div>
-<div id="d5"><math><semantics><mi>a</mi><annotation-xml><foo/><bar/></annotation-xml></semantics></math></div>
-<div id="d6"><math><semantics><mi>a</mi><annotation-xml encoding="text/html"><div></div></annotation-xml></semantics><mn/></math>
-</div>
-
-
-<script>
-
-test(function() {
-assert_equals(document.getElementById("m1"),document.getElementsByTagName("math")[0]);
-},"The id attribute should be recognised on math elements");
-
-test(function() {
-assert_equals(document.getElementById("d1").firstChild.nodeName,"math")
-},"The node name should be math");
-
-test(function() {
-assert_equals(document.getElementById("d1").firstChild.namespaceURI ,"http://www.w3.org/1998/Math/MathML")
-},"math should be in MathML Namespace");
-
-test(function() {
-assert_equals(document.getElementById("d1").firstChild.childNodes.length ,2)
-},"Math has 2 children (empty tag syntax)");
-
-test(function() {
-assert_equals(document.getElementById("d2").firstChild.childNodes.length ,1)
-},"Nested mrow elements should be parsed correctly");
-
-test(function() {
-assert_equals(document.getElementById("d3").firstChild.nodeValue ,"\u27E8\u27E9")
-},"Testing rang and lang entity code points");
-
-test(function() {
-assert_equals(document.getElementById("d4").firstChild.nodeValue ,"\uD835\uDD42")
-},"Testing Kopf (Plane 1) entity code point");
-
-test(function() {
-assert_equals(document.getElementById("d5").firstChild.firstChild.childNodes[1].childNodes.length ,2)
-},"Empty element tags in annotation-xml parsed as per XML.");
-
-test(function() {
-assert_equals(document.getElementById("d6").firstChild.childNodes.length ,2)
-},"html tags allowed in annotation-xml/@encoding='text/html'.");
-
-</script>