diff --git a/dom/base/TabGroup.cpp b/dom/base/TabGroup.cpp
index 3f6c903ea22f..5884bb6df7a7 100644
--- a/dom/base/TabGroup.cpp
+++ b/dom/base/TabGroup.cpp
@@ -9,6 +9,7 @@
 #include "mozilla/dom/ContentChild.h"
 #include "mozilla/dom/TabChild.h"
 #include "mozilla/dom/DocGroup.h"
+#include "mozilla/dom/TimeoutManager.h"
 #include "mozilla/AbstractThread.h"
 #include "mozilla/ClearOnShutdown.h"
 #include "mozilla/StaticPtr.h"
@@ -23,6 +24,8 @@ namespace dom {
 
 static StaticRefPtr<TabGroup> sChromeTabGroup;
 
+LinkedList<TabGroup>* TabGroup::sTabGroups = nullptr;
+
 TabGroup::TabGroup(bool aIsChrome)
  : mLastWindowLeft(false)
  , mThrottledQueuesInitialized(false)
@@ -31,6 +34,11 @@ TabGroup::TabGroup(bool aIsChrome)
  , mIsChrome(aIsChrome)
  , mForegroundCount(0)
 {
+  if (!sTabGroups) {
+    sTabGroups = new LinkedList<TabGroup>();
+  }
+  sTabGroups->insertBack(this);
+
   CreateEventTargets(/* aNeedValidation = */ !aIsChrome);
 
   // Do not throttle runnables from chrome windows.  In theory we should
@@ -54,6 +62,15 @@ TabGroup::~TabGroup()
   MOZ_ASSERT(mDocGroups.IsEmpty());
   MOZ_ASSERT(mWindows.IsEmpty());
   MOZ_RELEASE_ASSERT(mLastWindowLeft || mIsChrome);
+
+  LinkedListElement<TabGroup>* listElement =
+    static_cast<LinkedListElement<TabGroup>*>(this);
+  listElement->remove();
+
+  if (sTabGroups->isEmpty()) {
+    delete sTabGroups;
+    sTabGroups = nullptr;
+  }
 }
 
 void
@@ -323,5 +340,37 @@ TabGroup::Count(bool aActiveOnly) const
   return count;
 }
 
+/*static*/ bool
+TabGroup::HasOnlyThrottableTabs()
+{
+  if (!sTabGroups) {
+    return false;
+  }
+
+  for (TabGroup* tabGroup = sTabGroups->getFirst(); tabGroup;
+       tabGroup =
+         static_cast<LinkedListElement<TabGroup>*>(tabGroup)->getNext()) {
+    for (auto iter = tabGroup->Iter(); !iter.Done(); iter.Next()) {
+      DocGroup* docGroup = iter.Get()->mDocGroup;
+      for (auto* documentInDocGroup : *docGroup) {
+        if (documentInDocGroup->IsCurrentActiveDocument()) {
+          nsPIDOMWindowInner* win =
+            documentInDocGroup->GetInnerWindow();
+          if (win && win->IsCurrentInnerWindow()) {
+            nsPIDOMWindowOuter* outer = win->GetOuterWindow();
+            if (outer) {
+              TimeoutManager& tm = win->TimeoutManager();
+              if (!tm.BudgetThrottlingEnabled(outer->IsBackground())) {
+                return false;
+              }
+            }
+          }
+        }
+      }
+    }
+  }
+  return true;
+}
+
 } // namespace dom
 } // namespace mozilla
diff --git a/dom/base/TabGroup.h b/dom/base/TabGroup.h
index 153f652dc73e..9ed8eefe5056 100644
--- a/dom/base/TabGroup.h
+++ b/dom/base/TabGroup.h
@@ -46,7 +46,8 @@ class TabChild;
 class DocGroup;
 class TabChild;
 
-class TabGroup final : public SchedulerGroup
+class TabGroup final : public SchedulerGroup,
+                       public LinkedListElement<TabGroup>
 {
 private:
   class HashEntry : public nsCStringHashKey
@@ -146,6 +147,16 @@ public:
     return mNumOfIndexedDBDatabases;
   }
 
+  static LinkedList<TabGroup>* GetTabGroupList()
+  {
+    return sTabGroups;
+  }
+
+  // This returns true if all the window objects in all the TabGroups are
+  // either inactive (for example in bfcache) or are in background tabs which
+  // can be throttled.
+  static bool HasOnlyThrottableTabs();
+
 private:
   virtual AbstractThread*
   AbstractMainThreadForImpl(TaskCategory aCategory) override;
@@ -167,6 +178,8 @@ private:
   DocGroupMap mDocGroups;
   nsTArray<nsPIDOMWindowOuter*> mWindows;
   uint32_t mForegroundCount;
+
+  static LinkedList<TabGroup>* sTabGroups;
 };
 
 } // namespace dom
diff --git a/dom/base/TimeoutManager.h b/dom/base/TimeoutManager.h
index 6040f1ec2971..79c356bf096d 100644
--- a/dom/base/TimeoutManager.h
+++ b/dom/base/TimeoutManager.h
@@ -111,6 +111,8 @@ public:
   nsIEventTarget*
   EventTarget();
 
+  bool BudgetThrottlingEnabled(bool aIsBackground) const;
+
   static const uint32_t InvalidFiringId;
 
 private:
@@ -149,8 +151,6 @@ private:
   void UpdateBudget(const TimeStamp& aNow,
                     const TimeDuration& aDuration = TimeDuration());
 
-  bool BudgetThrottlingEnabled(bool aIsBackground) const;
-
 private:
   struct Timeouts {
     explicit Timeouts(const TimeoutManager& aManager)
diff --git a/dom/smil/nsSMILKeySpline.h b/dom/smil/nsSMILKeySpline.h
index 36c14fec1fef..c651c278fa5c 100644
--- a/dom/smil/nsSMILKeySpline.h
+++ b/dom/smil/nsSMILKeySpline.h
@@ -16,7 +16,14 @@
 class nsSMILKeySpline
 {
 public:
-  nsSMILKeySpline() { /* caller must call Init later */ }
+  nsSMILKeySpline()
+    : mX1(0)
+    , mY1(0)
+    , mX2(0)
+    , mY2(0)
+  { 
+    /* caller must call Init later */\
+  }
 
   /**
    * Creates a new key spline control point description.
@@ -26,6 +33,10 @@ public:
    */
   nsSMILKeySpline(double aX1, double aY1,
                   double aX2, double aY2)
+    : mX1(0)
+    , mY1(0)
+    , mX2(0)
+    , mY2(0)
   {
     Init(aX1, aY1, aX2, aY2);
   }
diff --git a/dom/smil/nsSMILValue.cpp b/dom/smil/nsSMILValue.cpp
index e5f904bb591e..fe67af84f2f9 100644
--- a/dom/smil/nsSMILValue.cpp
+++ b/dom/smil/nsSMILValue.cpp
@@ -14,6 +14,7 @@
 nsSMILValue::nsSMILValue(const nsISMILType* aType)
   : mType(nsSMILNullType::Singleton())
 {
+  mU.mBool = false;
   if (!aType) {
     NS_ERROR("Trying to construct nsSMILValue with null mType pointer");
     return;
diff --git a/dom/svg/DOMSVGPathSegList.h b/dom/svg/DOMSVGPathSegList.h
index 5683f5f6dd33..84bb5ef036fb 100644
--- a/dom/svg/DOMSVGPathSegList.h
+++ b/dom/svg/DOMSVGPathSegList.h
@@ -230,7 +230,10 @@ private:
    * want to create the DOMSVGPathSeg items lazily on demand.
    */
   struct ItemProxy {
-    ItemProxy(){}
+    ItemProxy()
+      : mItem(nullptr)
+      , mInternalDataIndex(0)
+    {}
     ItemProxy(DOMSVGPathSeg *aItem, uint32_t aInternalDataIndex)
       : mItem(aItem)
       , mInternalDataIndex(aInternalDataIndex)
diff --git a/dom/svg/SVGAnimatedNumberList.h b/dom/svg/SVGAnimatedNumberList.h
index 6b5e78c79c81..7300b286e51a 100644
--- a/dom/svg/SVGAnimatedNumberList.h
+++ b/dom/svg/SVGAnimatedNumberList.h
@@ -43,7 +43,9 @@ class SVGAnimatedNumberList
   friend class DOMSVGNumberList;
 
 public:
-  SVGAnimatedNumberList() {}
+  SVGAnimatedNumberList()
+    : mIsBaseSet(false)
+  {}
 
   /**
    * Because it's so important that mBaseVal and its DOMSVGNumberList wrapper
diff --git a/dom/svg/SVGGeometryElement.h b/dom/svg/SVGGeometryElement.h
index cef22975dade..54a7ea61412e 100644
--- a/dom/svg/SVGGeometryElement.h
+++ b/dom/svg/SVGGeometryElement.h
@@ -112,7 +112,11 @@ public:
   {
   public:
     SimplePath()
-      : mType(NONE)
+      : mX(0.0)
+      , mY(0.0)
+      , mWidthOrX2(0.0)
+      , mHeightOrY2(0.0)
+      , mType(NONE)
     {}
     bool IsPath() const {
       return mType != NONE;
diff --git a/dom/svg/SVGLength.h b/dom/svg/SVGLength.h
index 12757aa4fb58..6f4847be184e 100644
--- a/dom/svg/SVGLength.h
+++ b/dom/svg/SVGLength.h
@@ -33,10 +33,8 @@ class SVGLength
 public:
 
   SVGLength()
-#ifdef DEBUG
     : mValue(0.0f)
     , mUnit(dom::SVGLengthBinding::SVG_LENGTHTYPE_UNKNOWN) // caught by IsValid()
-#endif
   {}
 
   SVGLength(float aValue, uint8_t aUnit)
diff --git a/dom/svg/SVGLengthList.h b/dom/svg/SVGLengthList.h
index f9c8bd35613f..f74fb5ba6cf3 100644
--- a/dom/svg/SVGLengthList.h
+++ b/dom/svg/SVGLengthList.h
@@ -311,6 +311,8 @@ public:
 
   SVGUserUnitList()
     : mList(nullptr)
+    , mElement(nullptr)
+    , mAxis(0)
   {}
 
   void Init(const SVGLengthList *aList, nsSVGElement *aElement, uint8_t aAxis) {
diff --git a/dom/svg/SVGMotionSMILType.cpp b/dom/svg/SVGMotionSMILType.cpp
index 4b29f882a72f..524d4672bd7e 100644
--- a/dom/svg/SVGMotionSMILType.cpp
+++ b/dom/svg/SVGMotionSMILType.cpp
@@ -64,7 +64,10 @@ struct MotionSegment
   // Default constructor just locks us into being a Translation, and leaves
   // other fields uninitialized (since client is presumably about to set them)
   MotionSegment()
-    : mSegmentType(eSegmentType_Translation)
+    : mRotateType(eRotateType_Auto),
+      mRotateAngle(0.0),
+      mSegmentType(eSegmentType_Translation),
+      mU{}
   { }
 
   // Constructor for a translation
diff --git a/dom/svg/nsSVGViewBox.h b/dom/svg/nsSVGViewBox.h
index edf511e983d3..a0725a92d305 100644
--- a/dom/svg/nsSVGViewBox.h
+++ b/dom/svg/nsSVGViewBox.h
@@ -32,7 +32,13 @@ struct nsSVGViewBoxRect
   float width, height;
   bool none;
 
-  nsSVGViewBoxRect() : none(true) {}
+  nsSVGViewBoxRect()
+    : x(0.0)
+    , y(0.0)
+    , width(0.0)
+    , height(0.0)
+    , none(true)
+  {}
   nsSVGViewBoxRect(float aX, float aY, float aWidth, float aHeight) :
     x(aX), y(aY), width(aWidth), height(aHeight), none(false) {}
   nsSVGViewBoxRect(const nsSVGViewBoxRect& rhs) :
diff --git a/js/src/builtin/ReflectParse.cpp b/js/src/builtin/ReflectParse.cpp
index 1f052be21706..44a5cf9bf99f 100644
--- a/js/src/builtin/ReflectParse.cpp
+++ b/js/src/builtin/ReflectParse.cpp
@@ -282,8 +282,7 @@ class NodeBuilder
             }
 
             if (!funv.isObject() || !funv.toObject().is<JSFunction>()) {
-                ReportValueErrorFlags(cx, JSREPORT_ERROR, JSMSG_NOT_FUNCTION,
-                                      JSDVG_SEARCH_STACK, funv, nullptr, nullptr, nullptr);
+                ReportValueError(cx, JSMSG_NOT_FUNCTION, JSDVG_SEARCH_STACK, funv, nullptr);
                 return false;
             }
 
@@ -3362,9 +3361,8 @@ reflect_parse(JSContext* cx, uint32_t argc, Value* vp)
 
     if (!arg.isNullOrUndefined()) {
         if (!arg.isObject()) {
-            ReportValueErrorFlags(cx, JSREPORT_ERROR, JSMSG_UNEXPECTED_TYPE,
-                                  JSDVG_SEARCH_STACK, arg, nullptr,
-                                  "not an object", nullptr);
+            ReportValueError(cx, JSMSG_UNEXPECTED_TYPE, JSDVG_SEARCH_STACK, arg, nullptr,
+                             "not an object");
             return false;
         }
 
@@ -3414,9 +3412,8 @@ reflect_parse(JSContext* cx, uint32_t argc, Value* vp)
 
         if (!prop.isNullOrUndefined()) {
             if (!prop.isObject()) {
-                ReportValueErrorFlags(cx, JSREPORT_ERROR, JSMSG_UNEXPECTED_TYPE,
-                                      JSDVG_SEARCH_STACK, prop, nullptr,
-                                      "not an object", nullptr);
+                ReportValueError(cx, JSMSG_UNEXPECTED_TYPE, JSDVG_SEARCH_STACK, prop, nullptr,
+                                 "not an object");
                 return false;
             }
             builder = &prop.toObject();
@@ -3429,8 +3426,8 @@ reflect_parse(JSContext* cx, uint32_t argc, Value* vp)
             return false;
 
         if (!prop.isString()) {
-            ReportValueErrorFlags(cx, JSREPORT_ERROR, JSMSG_UNEXPECTED_TYPE, JSDVG_SEARCH_STACK,
-                                  prop, nullptr, "not 'script' or 'module'", nullptr);
+            ReportValueError(cx, JSMSG_UNEXPECTED_TYPE, JSDVG_SEARCH_STACK, prop, nullptr,
+                             "not 'script' or 'module'");
             return false;
         }
 
diff --git a/js/src/builtin/Stream.cpp b/js/src/builtin/Stream.cpp
index 1e6c01ad5f7a..0a0407f581b1 100644
--- a/js/src/builtin/Stream.cpp
+++ b/js/src/builtin/Stream.cpp
@@ -270,17 +270,15 @@ PromiseRejectedWithPendingError(JSContext* cx) {
     return PromiseObject::unforgeableReject(cx, exn);
 }
 
-static bool
-ReportArgTypeError(JSContext* cx, const char* funName, const char* expectedType,
-                   HandleValue arg)
+static void
+ReportArgTypeError(JSContext* cx, const char* funName, const char* expectedType, HandleValue arg)
 {
     UniqueChars bytes = DecompileValueGenerator(cx, JSDVG_SEARCH_STACK, arg, nullptr);
     if (!bytes)
-        return false;
+        return;
 
-    return JS_ReportErrorFlagsAndNumberLatin1(cx, JSREPORT_ERROR, GetErrorMessage,
-                                              nullptr, JSMSG_NOT_EXPECTED_TYPE,
-                                              funName, expectedType, bytes.get());
+    JS_ReportErrorNumberLatin1(cx, GetErrorMessage, nullptr, JSMSG_NOT_EXPECTED_TYPE, funName,
+                               expectedType, bytes.get());
 }
 
 static MOZ_MUST_USE bool
@@ -307,8 +305,8 @@ static MOZ_MUST_USE bool
 RejectNonGenericMethod(JSContext* cx, const CallArgs& args,
                        const char* className, const char* methodName)
 {
-    ReportValueError3(cx, JSMSG_INCOMPATIBLE_PROTO, JSDVG_SEARCH_STACK, args.thisv(),
-                      nullptr, className, methodName);
+    ReportValueError(cx, JSMSG_INCOMPATIBLE_PROTO, JSDVG_SEARCH_STACK, args.thisv(),
+                     nullptr, className, methodName);
 
     return ReturnPromiseRejectedWithPendingError(cx, args);
 }
@@ -803,8 +801,8 @@ ReadableStream_cancel(JSContext* cx, unsigned argc, Value* vp)
     // Step 1: If ! IsReadableStream(this) is false, return a promise rejected
     //         with a TypeError exception.
     if (!Is<ReadableStream>(args.thisv())) {
-        ReportValueError3(cx, JSMSG_INCOMPATIBLE_PROTO, JSDVG_SEARCH_STACK, args.thisv(),
-                          nullptr, "cancel", "");
+        ReportValueError(cx, JSMSG_INCOMPATIBLE_PROTO, JSDVG_SEARCH_STACK, args.thisv(),
+                         nullptr, "cancel", "");
         return ReturnPromiseRejectedWithPendingError(cx, args);
     }
 
diff --git a/js/src/builtin/Symbol.cpp b/js/src/builtin/Symbol.cpp
index a6f4314c9fbc..411e7b2528d6 100644
--- a/js/src/builtin/Symbol.cpp
+++ b/js/src/builtin/Symbol.cpp
@@ -150,8 +150,8 @@ SymbolObject::keyFor(JSContext* cx, unsigned argc, Value* vp)
     // step 1
     HandleValue arg = args.get(0);
     if (!arg.isSymbol()) {
-        ReportValueErrorFlags(cx, JSREPORT_ERROR, JSMSG_UNEXPECTED_TYPE, JSDVG_SEARCH_STACK,
-                              arg, nullptr, "not a symbol", nullptr);
+        ReportValueError(cx, JSMSG_UNEXPECTED_TYPE, JSDVG_SEARCH_STACK, arg, nullptr,
+                         "not a symbol");
         return false;
     }
 
diff --git a/js/src/builtin/TestingFunctions.cpp b/js/src/builtin/TestingFunctions.cpp
index 8a28368c3819..fa102fdcb1d4 100644
--- a/js/src/builtin/TestingFunctions.cpp
+++ b/js/src/builtin/TestingFunctions.cpp
@@ -1304,9 +1304,8 @@ SaveStack(JSContext* cx, unsigned argc, Value* vp)
         if (!ToNumber(cx, args[0], &maxDouble))
             return false;
         if (mozilla::IsNaN(maxDouble) || maxDouble < 0 || maxDouble > UINT32_MAX) {
-            ReportValueErrorFlags(cx, JSREPORT_ERROR, JSMSG_UNEXPECTED_TYPE,
-                                  JSDVG_SEARCH_STACK, args[0], nullptr,
-                                  "not a valid maximum frame count", NULL);
+            ReportValueError(cx, JSMSG_UNEXPECTED_TYPE, JSDVG_SEARCH_STACK, args[0], nullptr,
+                             "not a valid maximum frame count");
             return false;
         }
         uint32_t max = uint32_t(maxDouble);
@@ -1317,9 +1316,8 @@ SaveStack(JSContext* cx, unsigned argc, Value* vp)
     RootedObject compartmentObject(cx);
     if (args.length() >= 2) {
         if (!args[1].isObject()) {
-            ReportValueErrorFlags(cx, JSREPORT_ERROR, JSMSG_UNEXPECTED_TYPE,
-                                  JSDVG_SEARCH_STACK, args[0], nullptr,
-                                  "not an object", NULL);
+            ReportValueError(cx, JSMSG_UNEXPECTED_TYPE, JSDVG_SEARCH_STACK, args[0], nullptr,
+                             "not an object");
             return false;
         }
         compartmentObject = UncheckedUnwrap(&args[1].toObject());
@@ -3593,16 +3591,14 @@ FindPath(JSContext* cx, unsigned argc, Value* vp)
     // test is all about object identity, and ToString doesn't preserve that.
     // Non-GCThing endpoints don't make much sense.
     if (!args[0].isObject() && !args[0].isString() && !args[0].isSymbol()) {
-        ReportValueErrorFlags(cx, JSREPORT_ERROR, JSMSG_UNEXPECTED_TYPE,
-                              JSDVG_SEARCH_STACK, args[0], nullptr,
-                              "not an object, string, or symbol", NULL);
+        ReportValueError(cx, JSMSG_UNEXPECTED_TYPE, JSDVG_SEARCH_STACK, args[0], nullptr,
+                         "not an object, string, or symbol");
         return false;
     }
 
     if (!args[1].isObject() && !args[1].isString() && !args[1].isSymbol()) {
-        ReportValueErrorFlags(cx, JSREPORT_ERROR, JSMSG_UNEXPECTED_TYPE,
-                              JSDVG_SEARCH_STACK, args[0], nullptr,
-                              "not an object, string, or symbol", NULL);
+        ReportValueError(cx, JSMSG_UNEXPECTED_TYPE, JSDVG_SEARCH_STACK, args[0], nullptr,
+                         "not an object, string, or symbol");
         return false;
     }
 
@@ -3698,25 +3694,22 @@ ShortestPaths(JSContext* cx, unsigned argc, Value* vp)
     // test is all about object identity, and ToString doesn't preserve that.
     // Non-GCThing endpoints don't make much sense.
     if (!args[0].isObject() && !args[0].isString() && !args[0].isSymbol()) {
-        ReportValueErrorFlags(cx, JSREPORT_ERROR, JSMSG_UNEXPECTED_TYPE,
-                              JSDVG_SEARCH_STACK, args[0], nullptr,
-                              "not an object, string, or symbol", nullptr);
+        ReportValueError(cx, JSMSG_UNEXPECTED_TYPE, JSDVG_SEARCH_STACK, args[0], nullptr,
+                         "not an object, string, or symbol");
         return false;
     }
 
     if (!args[1].isObject() || !args[1].toObject().is<ArrayObject>()) {
-        ReportValueErrorFlags(cx, JSREPORT_ERROR, JSMSG_UNEXPECTED_TYPE,
-                              JSDVG_SEARCH_STACK, args[1], nullptr,
-                              "not an array object", nullptr);
+        ReportValueError(cx, JSMSG_UNEXPECTED_TYPE, JSDVG_SEARCH_STACK, args[1], nullptr,
+                         "not an array object");
         return false;
     }
 
     RootedArrayObject objs(cx, &args[1].toObject().as<ArrayObject>());
     size_t length = objs->getDenseInitializedLength();
     if (length == 0) {
-        ReportValueErrorFlags(cx, JSREPORT_ERROR, JSMSG_UNEXPECTED_TYPE,
-                              JSDVG_SEARCH_STACK, args[1], nullptr,
-                              "not a dense array object with one or more elements", nullptr);
+        ReportValueError(cx, JSMSG_UNEXPECTED_TYPE, JSDVG_SEARCH_STACK, args[1], nullptr,
+                         "not a dense array object with one or more elements");
         return false;
     }
 
@@ -3732,9 +3725,8 @@ ShortestPaths(JSContext* cx, unsigned argc, Value* vp)
     if (!JS::ToInt32(cx, args[2], &maxNumPaths))
         return false;
     if (maxNumPaths <= 0) {
-        ReportValueErrorFlags(cx, JSREPORT_ERROR, JSMSG_UNEXPECTED_TYPE,
-                              JSDVG_SEARCH_STACK, args[2], nullptr,
-                              "not greater than 0", nullptr);
+        ReportValueError(cx, JSMSG_UNEXPECTED_TYPE, JSDVG_SEARCH_STACK, args[2], nullptr,
+                         "not greater than 0");
         return false;
     }
 
diff --git a/js/src/ctypes/CTypes.cpp b/js/src/ctypes/CTypes.cpp
index 0bac9d266abe..806ad08847cd 100644
--- a/js/src/ctypes/CTypes.cpp
+++ b/js/src/ctypes/CTypes.cpp
@@ -97,10 +97,8 @@ GetDeflatedUTF8StringLength(JSContext* maybecx, const CharT* chars,
         js::gc::AutoSuppressGC suppress(maybecx);
         char buffer[10];
         SprintfLiteral(buffer, "0x%x", c);
-        JS_ReportErrorFlagsAndNumberASCII(maybecx, JSREPORT_ERROR,
-                                          GetErrorMessage,
-                                          nullptr, JSMSG_BAD_SURROGATE_CHAR,
-                                          buffer);
+        JS_ReportErrorNumberASCII(maybecx, GetErrorMessage, nullptr, JSMSG_BAD_SURROGATE_CHAR,
+                                  buffer);
     }
     return (size_t) -1;
 }
diff --git a/js/src/jsapi.cpp b/js/src/jsapi.cpp
index c300848f7682..9f83f5cea4c0 100644
--- a/js/src/jsapi.cpp
+++ b/js/src/jsapi.cpp
@@ -7093,7 +7093,7 @@ JSErrorNotes::copy(JSContext* cx)
     }
 
     for (auto&& note : *this) {
-        js::UniquePtr<JSErrorNotes::Note> copied(CopyErrorNote(cx, note.get()));
+        UniquePtr<JSErrorNotes::Note> copied = CopyErrorNote(cx, note.get());
         if (!copied)
             return nullptr;
 
diff --git a/js/src/jsapi.h b/js/src/jsapi.h
index 91d585842fc8..b82842ad3fa3 100644
--- a/js/src/jsapi.h
+++ b/js/src/jsapi.h
@@ -495,13 +495,6 @@ static const unsigned JSFUN_CONSTRUCTOR =     0x400;
 /* | of all the JSFUN_* flags */
 static const unsigned JSFUN_FLAGS_MASK =      0x400;
 
-/*
- * If set, will allow redefining a non-configurable property, but only on a
- * non-DOM global.  This is a temporary hack that will need to go away in bug
- * 1105518.
- */
-static const unsigned JSPROP_REDEFINE_NONCONFIGURABLE = 0x1000;
-
 /*
  * Resolve hooks and enumerate hooks must pass this flag when calling
  * JS_Define* APIs to reify lazily-defined properties.
@@ -2112,7 +2105,6 @@ class WrappedPtrOperations<JS::PropertyDescriptor, Wrapper>
                                      JSPROP_IGNORE_VALUE |
                                      JSPROP_GETTER |
                                      JSPROP_SETTER |
-                                     JSPROP_REDEFINE_NONCONFIGURABLE |
                                      JSPROP_RESOLVING |
                                      SHADOWABLE)) == 0);
         MOZ_ASSERT(!hasAll(JSPROP_IGNORE_ENUMERATE | JSPROP_ENUMERATE));
@@ -2134,7 +2126,6 @@ class WrappedPtrOperations<JS::PropertyDescriptor, Wrapper>
         MOZ_ASSERT_IF(has(JSPROP_RESOLVING), !has(JSPROP_IGNORE_PERMANENT));
         MOZ_ASSERT_IF(has(JSPROP_RESOLVING), !has(JSPROP_IGNORE_READONLY));
         MOZ_ASSERT_IF(has(JSPROP_RESOLVING), !has(JSPROP_IGNORE_VALUE));
-        MOZ_ASSERT_IF(has(JSPROP_RESOLVING), !has(JSPROP_REDEFINE_NONCONFIGURABLE));
 #endif
     }
 
@@ -2146,7 +2137,6 @@ class WrappedPtrOperations<JS::PropertyDescriptor, Wrapper>
                                      JSPROP_READONLY |
                                      JSPROP_GETTER |
                                      JSPROP_SETTER |
-                                     JSPROP_REDEFINE_NONCONFIGURABLE |
                                      JSPROP_RESOLVING |
                                      SHADOWABLE)) == 0);
         MOZ_ASSERT_IF(isAccessorDescriptor(), has(JSPROP_GETTER) && has(JSPROP_SETTER));
diff --git a/js/src/jsdate.cpp b/js/src/jsdate.cpp
index 2a2502656796..5e1a540a7b25 100644
--- a/js/src/jsdate.cpp
+++ b/js/src/jsdate.cpp
@@ -2654,8 +2654,7 @@ date_toJSON(JSContext* cx, unsigned argc, Value* vp)
 
     /* Step 5. */
     if (!IsCallable(toISO)) {
-        JS_ReportErrorFlagsAndNumberASCII(cx, JSREPORT_ERROR, js::GetErrorMessage, nullptr,
-                                          JSMSG_BAD_TOISOSTRING_PROP);
+        JS_ReportErrorNumberASCII(cx, js::GetErrorMessage, nullptr, JSMSG_BAD_TOISOSTRING_PROP);
         return false;
     }
 
diff --git a/js/src/jsexn.cpp b/js/src/jsexn.cpp
index dafd663091fc..4bd5a96185cc 100644
--- a/js/src/jsexn.cpp
+++ b/js/src/jsexn.cpp
@@ -14,6 +14,7 @@
 #include "mozilla/Sprintf.h"
 
 #include <string.h>
+#include <utility>
 
 #include "jsapi.h"
 #include "jsnum.h"
@@ -23,6 +24,7 @@
 #include "gc/FreeOp.h"
 #include "gc/Marking.h"
 #include "js/CharacterEncoding.h"
+#include "js/UniquePtr.h"
 #include "js/Wrapper.h"
 #include "util/StringBuffer.h"
 #include "vm/ErrorObject.h"
@@ -267,7 +269,7 @@ CopyExtraData(JSContext* cx, uint8_t** cursor, JSErrorNotes::Note* copy, JSError
 }
 
 template <typename T>
-static T*
+static UniquePtr<T>
 CopyErrorHelper(JSContext* cx, T* report)
 {
     /*
@@ -298,7 +300,7 @@ CopyErrorHelper(JSContext* cx, T* report)
     if (!cursor)
         return nullptr;
 
-    T* copy = new (cursor) T();
+    UniquePtr<T> copy(new (cursor) T());
     cursor += sizeof(T);
 
     if (report->message()) {
@@ -313,13 +315,10 @@ CopyErrorHelper(JSContext* cx, T* report)
         cursor += filenameSize;
     }
 
-    if (!CopyExtraData(cx, &cursor, copy, report)) {
-        /* js_delete calls destructor for T and js_free for pod_calloc. */
-        js_delete(copy);
+    if (!CopyExtraData(cx, &cursor, copy.get(), report))
         return nullptr;
-    }
 
-    MOZ_ASSERT(cursor == (uint8_t*)copy + mallocSize);
+    MOZ_ASSERT(cursor == (uint8_t*)copy.get() + mallocSize);
 
     /* Copy non-pointer members. */
     copy->lineno = report->lineno;
@@ -329,13 +328,13 @@ CopyErrorHelper(JSContext* cx, T* report)
     return copy;
 }
 
-JSErrorNotes::Note*
+UniquePtr<JSErrorNotes::Note>
 js::CopyErrorNote(JSContext* cx, JSErrorNotes::Note* note)
 {
     return CopyErrorHelper(cx, note);
 }
 
-JSErrorReport*
+UniquePtr<JSErrorReport>
 js::CopyErrorReport(JSContext* cx, JSErrorReport* report)
 {
     return CopyErrorHelper(cx, report);
@@ -686,12 +685,12 @@ js::ErrorToException(JSContext* cx, JSErrorReport* reportp,
     if (!CaptureStack(cx, &stack))
         return;
 
-    js::ScopedJSFreePtr<JSErrorReport> report(CopyErrorReport(cx, reportp));
+    UniquePtr<JSErrorReport> report = CopyErrorReport(cx, reportp);
     if (!report)
         return;
 
-    RootedObject errObject(cx, ErrorObject::create(cx, exnType, stack, fileName,
-                                                   lineNumber, columnNumber, &report, messageStr));
+    RootedObject errObject(cx, ErrorObject::create(cx, exnType, stack, fileName, lineNumber,
+                                                   columnNumber, std::move(report), messageStr));
     if (!errObject)
         return;
 
@@ -990,7 +989,7 @@ ErrorReport::populateUncaughtExceptionReportUTF8VA(JSContext* cx, va_list ap)
 JSObject*
 js::CopyErrorObject(JSContext* cx, Handle<ErrorObject*> err)
 {
-    js::ScopedJSFreePtr<JSErrorReport> copyReport;
+    UniquePtr<JSErrorReport> copyReport;
     if (JSErrorReport* errorReport = err->getErrorReport()) {
         copyReport = CopyErrorReport(cx, errorReport);
         if (!copyReport)
@@ -1012,7 +1011,7 @@ js::CopyErrorObject(JSContext* cx, Handle<ErrorObject*> err)
 
     // Create the Error object.
     return ErrorObject::create(cx, errorType, stack, fileName,
-                               lineNumber, columnNumber, &copyReport, message);
+                               lineNumber, columnNumber, std::move(copyReport), message);
 }
 
 JS_PUBLIC_API(bool)
@@ -1023,13 +1022,15 @@ JS::CreateError(JSContext* cx, JSExnType type, HandleObject stack, HandleString
     assertSameCompartment(cx, stack, fileName, message);
     AssertObjectIsSavedFrameOrWrapper(cx, stack);
 
-    js::ScopedJSFreePtr<JSErrorReport> rep;
-    if (report)
+    js::UniquePtr<JSErrorReport> rep;
+    if (report) {
         rep = CopyErrorReport(cx, report);
+        if (!rep)
+            return false;
+    }
 
-    RootedObject obj(cx,
-        js::ErrorObject::create(cx, type, stack, fileName,
-                                lineNumber, columnNumber, &rep, message));
+    JSObject* obj = js::ErrorObject::create(cx, type, stack, fileName, lineNumber, columnNumber,
+                                            std::move(rep), message);
     if (!obj)
         return false;
 
diff --git a/js/src/jsexn.h b/js/src/jsexn.h
index 233bcf6efbfd..f7fc36231701 100644
--- a/js/src/jsexn.h
+++ b/js/src/jsexn.h
@@ -14,15 +14,16 @@
 #include "jsapi.h"
 #include "NamespaceImports.h"
 
+#include "js/UniquePtr.h"
 #include "vm/JSContext.h"
 
 namespace js {
 class ErrorObject;
 
-JSErrorNotes::Note*
+UniquePtr<JSErrorNotes::Note>
 CopyErrorNote(JSContext* cx, JSErrorNotes::Note* note);
 
-JSErrorReport*
+UniquePtr<JSErrorReport>
 CopyErrorReport(JSContext* cx, JSErrorReport* report);
 
 JSString*
diff --git a/js/src/vm/CharacterEncoding.cpp b/js/src/vm/CharacterEncoding.cpp
index fea6dc566500..b041455f867c 100644
--- a/js/src/vm/CharacterEncoding.cpp
+++ b/js/src/vm/CharacterEncoding.cpp
@@ -230,8 +230,7 @@ ReportInvalidCharacter(JSContext* cx, uint32_t offset)
 {
     char buffer[10];
     SprintfLiteral(buffer, "%u", offset);
-    JS_ReportErrorFlagsAndNumberASCII(cx, JSREPORT_ERROR, GetErrorMessage, nullptr,
-                                      JSMSG_MALFORMED_UTF8_CHAR, buffer);
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr, JSMSG_MALFORMED_UTF8_CHAR, buffer);
 }
 
 static void
@@ -245,8 +244,7 @@ ReportTooBigCharacter(JSContext* cx, uint32_t v)
 {
     char buffer[10];
     SprintfLiteral(buffer, "0x%x", v + 0x10000);
-    JS_ReportErrorFlagsAndNumberASCII(cx, JSREPORT_ERROR, GetErrorMessage, nullptr,
-                                      JSMSG_UTF8_CHAR_TOO_LARGE, buffer);
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr, JSMSG_UTF8_CHAR_TOO_LARGE, buffer);
 }
 
 enum InflateUTF8Action {
diff --git a/js/src/vm/Debugger.cpp b/js/src/vm/Debugger.cpp
index 5bdbb6241a89..9bb6b8638b3e 100644
--- a/js/src/vm/Debugger.cpp
+++ b/js/src/vm/Debugger.cpp
@@ -274,9 +274,8 @@ ValueToIdentifier(JSContext* cx, HandleValue v, MutableHandleId id)
         return false;
     if (!JSID_IS_ATOM(id) || !IsIdentifier(JSID_TO_ATOM(id))) {
         RootedValue val(cx, v);
-        ReportValueErrorFlags(cx, JSREPORT_ERROR, JSMSG_UNEXPECTED_TYPE,
-                              JSDVG_SEARCH_STACK, val, nullptr, "not an identifier",
-                              nullptr);
+        ReportValueError(cx, JSMSG_UNEXPECTED_TYPE, JSDVG_SEARCH_STACK, val, nullptr,
+                         "not an identifier");
         return false;
     }
     return true;
@@ -522,13 +521,11 @@ RequireGlobalObject(JSContext* cx, HandleValue dbgobj, HandleObject referent)
         }
 
         if (obj->is<GlobalObject>()) {
-            ReportValueErrorFlags(cx, JSREPORT_ERROR, JSMSG_DEBUG_WRAPPER_IN_WAY,
-                                  JSDVG_SEARCH_STACK, dbgobj, nullptr,
-                                  isWrapper, isWindowProxy);
+            ReportValueError(cx, JSMSG_DEBUG_WRAPPER_IN_WAY, JSDVG_SEARCH_STACK, dbgobj, nullptr,
+                             isWrapper, isWindowProxy);
         } else {
-            ReportValueErrorFlags(cx, JSREPORT_ERROR, JSMSG_DEBUG_BAD_REFERENT,
-                                  JSDVG_SEARCH_STACK, dbgobj, nullptr,
-                                  "a global object", nullptr);
+            ReportValueError(cx, JSMSG_DEBUG_BAD_REFERENT, JSDVG_SEARCH_STACK, dbgobj, nullptr,
+                             "a global object");
         }
         return false;
     }
@@ -5361,9 +5358,8 @@ DebuggerScript_checkThis(JSContext* cx, const CallArgs& args, const char* fnname
         return nullptr;
 
     if (!GetScriptReferent(thisobj).is<ReferentT>()) {
-        ReportValueErrorFlags(cx, JSREPORT_ERROR, JSMSG_DEBUG_BAD_REFERENT,
-                              JSDVG_SEARCH_STACK, args.thisv(), nullptr,
-                              refname, nullptr);
+        ReportValueError(cx, JSMSG_DEBUG_BAD_REFERENT, JSDVG_SEARCH_STACK, args.thisv(), nullptr,
+                         refname);
         return nullptr;
     }
 
@@ -7007,9 +7003,8 @@ DebuggerSource_checkThis(JSContext* cx, const CallArgs& args, const char* fnname
         return nullptr;
 
     if (!GetSourceReferent(thisobj).is<ReferentT>()) {
-        ReportValueErrorFlags(cx, JSREPORT_ERROR, JSMSG_DEBUG_BAD_REFERENT,
-                              JSDVG_SEARCH_STACK, args.thisv(), nullptr,
-                              refname, nullptr);
+        ReportValueError(cx, JSMSG_DEBUG_BAD_REFERENT, JSDVG_SEARCH_STACK, args.thisv(), nullptr,
+                         refname);
         return nullptr;
     }
 
@@ -7092,9 +7087,8 @@ DebuggerSource_getBinary(JSContext* cx, unsigned argc, Value* vp)
     THIS_DEBUGSOURCE_REFERENT(cx, argc, vp, "(get binary)", args, obj, referent);
 
     if (!referent.is<WasmInstanceObject*>()) {
-        ReportValueErrorFlags(cx, JSREPORT_ERROR, JSMSG_DEBUG_BAD_REFERENT,
-                              JSDVG_SEARCH_STACK, args.thisv(), nullptr,
-                              "a wasm source", nullptr);
+        ReportValueError(cx, JSMSG_DEBUG_BAD_REFERENT, JSDVG_SEARCH_STACK, args.thisv(), nullptr,
+                         "a wasm source");
         return false;
     }
 
@@ -8097,9 +8091,8 @@ DebuggerFrame::requireScriptReferent(JSContext* cx, HandleDebuggerFrame frame)
     AbstractFramePtr referent = DebuggerFrame::getReferent(frame);
     if (!referent.hasScript()) {
         RootedValue frameobj(cx, ObjectValue(*frame));
-        ReportValueErrorFlags(cx, JSREPORT_ERROR, JSMSG_DEBUG_BAD_REFERENT,
-                              JSDVG_SEARCH_STACK, frameobj, nullptr,
-                              "a script frame", nullptr);
+        ReportValueError(cx, JSMSG_DEBUG_BAD_REFERENT, JSDVG_SEARCH_STACK, frameobj, nullptr,
+                         "a script frame");
         return false;
     }
     return true;
@@ -10707,13 +10700,11 @@ DebuggerObject::requireGlobal(JSContext* cx, HandleDebuggerObject object)
 
         RootedValue dbgobj(cx, ObjectValue(*object));
         if (referent->is<GlobalObject>()) {
-            ReportValueErrorFlags(cx, JSREPORT_ERROR, JSMSG_DEBUG_WRAPPER_IN_WAY,
-                                  JSDVG_SEARCH_STACK, dbgobj, nullptr,
-                                  isWrapper, isWindowProxy);
+            ReportValueError(cx, JSMSG_DEBUG_WRAPPER_IN_WAY, JSDVG_SEARCH_STACK, dbgobj, nullptr,
+                             isWrapper, isWindowProxy);
         } else {
-            ReportValueErrorFlags(cx, JSREPORT_ERROR, JSMSG_DEBUG_BAD_REFERENT,
-                                  JSDVG_SEARCH_STACK, dbgobj, nullptr,
-                                  "a global object", nullptr);
+            ReportValueError(cx, JSMSG_DEBUG_BAD_REFERENT, JSDVG_SEARCH_STACK, dbgobj, nullptr,
+                             "a global object");
         }
         return false;
     }
diff --git a/js/src/vm/ErrorObject.cpp b/js/src/vm/ErrorObject.cpp
index dfa3526184b6..307ac897ec80 100644
--- a/js/src/vm/ErrorObject.cpp
+++ b/js/src/vm/ErrorObject.cpp
@@ -9,6 +9,8 @@
 
 #include "mozilla/Range.h"
 
+#include <utility>
+
 #include "jsexn.h"
 
 #include "js/CallArgs.h"
@@ -38,7 +40,7 @@ js::ErrorObject::assignInitialShape(JSContext* cx, Handle<ErrorObject*> obj)
 
 /* static */ bool
 js::ErrorObject::init(JSContext* cx, Handle<ErrorObject*> obj, JSExnType type,
-                      ScopedJSFreePtr<JSErrorReport>* errorReport, HandleString fileName,
+                      UniquePtr<JSErrorReport> errorReport, HandleString fileName,
                       HandleObject stack, uint32_t lineNumber, uint32_t columnNumber,
                       HandleString message)
 {
@@ -72,7 +74,7 @@ js::ErrorObject::init(JSContext* cx, Handle<ErrorObject*> obj, JSExnType type,
 
     MOZ_ASSERT(JSEXN_ERR <= type && type < JSEXN_LIMIT);
 
-    JSErrorReport* report = errorReport ? errorReport->forget() : nullptr;
+    JSErrorReport* report = errorReport.release();
     obj->initReservedSlot(EXNTYPE_SLOT, Int32Value(type));
     obj->initReservedSlot(STACK_SLOT, ObjectOrNullValue(stack));
     obj->setReservedSlot(ERROR_REPORT_SLOT, PrivateValue(report));
@@ -88,7 +90,7 @@ js::ErrorObject::init(JSContext* cx, Handle<ErrorObject*> obj, JSExnType type,
 /* static */ ErrorObject*
 js::ErrorObject::create(JSContext* cx, JSExnType errorType, HandleObject stack,
                         HandleString fileName, uint32_t lineNumber, uint32_t columnNumber,
-                        ScopedJSFreePtr<JSErrorReport>* report, HandleString message,
+                        UniquePtr<JSErrorReport> report, HandleString message,
                         HandleObject protoArg /* = nullptr */)
 {
     AssertObjectIsSavedFrameOrWrapper(cx, stack);
@@ -109,7 +111,7 @@ js::ErrorObject::create(JSContext* cx, JSExnType errorType, HandleObject stack,
         errObject = &obj->as<ErrorObject>();
     }
 
-    if (!ErrorObject::init(cx, errObject, errorType, report, fileName, stack,
+    if (!ErrorObject::init(cx, errObject, errorType, std::move(report), fileName, stack,
                            lineNumber, columnNumber, message))
     {
         return nullptr;
@@ -156,11 +158,11 @@ js::ErrorObject::getOrCreateErrorReport(JSContext* cx)
     report.initOwnedMessage(utf8.release());
 
     // Cache and return.
-    JSErrorReport* copy = CopyErrorReport(cx, &report);
+    UniquePtr<JSErrorReport> copy = CopyErrorReport(cx, &report);
     if (!copy)
         return nullptr;
-    setReservedSlot(ERROR_REPORT_SLOT, PrivateValue(copy));
-    return copy;
+    setReservedSlot(ERROR_REPORT_SLOT, PrivateValue(copy.get()));
+    return copy.release();
 }
 
 static bool
diff --git a/js/src/vm/ErrorObject.h b/js/src/vm/ErrorObject.h
index 2e2427a388d5..0727235dd16a 100644
--- a/js/src/vm/ErrorObject.h
+++ b/js/src/vm/ErrorObject.h
@@ -9,6 +9,7 @@
 
 #include "mozilla/ArrayUtils.h"
 
+#include "js/UniquePtr.h"
 #include "vm/NativeObject.h"
 #include "vm/SavedStacks.h"
 #include "vm/Shape.h"
@@ -35,7 +36,7 @@ class ErrorObject : public NativeObject
 
     static bool
     init(JSContext* cx, Handle<ErrorObject*> obj, JSExnType type,
-         ScopedJSFreePtr<JSErrorReport>* errorReport, HandleString fileName, HandleObject stack,
+         UniquePtr<JSErrorReport> errorReport, HandleString fileName, HandleObject stack,
          uint32_t lineNumber, uint32_t columnNumber, HandleString message);
 
     static const ClassSpec classSpecs[JSEXN_ERROR_LIMIT];
@@ -70,7 +71,7 @@ class ErrorObject : public NativeObject
     // property.
     static ErrorObject*
     create(JSContext* cx, JSExnType type, HandleObject stack, HandleString fileName,
-           uint32_t lineNumber, uint32_t columnNumber, ScopedJSFreePtr<JSErrorReport>* report,
+           uint32_t lineNumber, uint32_t columnNumber, UniquePtr<JSErrorReport> report,
            HandleString message, HandleObject proto = nullptr);
 
     /*
diff --git a/js/src/vm/Interpreter.cpp b/js/src/vm/Interpreter.cpp
index 054d28c54313..85b68ab1f05f 100644
--- a/js/src/vm/Interpreter.cpp
+++ b/js/src/vm/Interpreter.cpp
@@ -994,7 +994,7 @@ js::CheckClassHeritageOperation(JSContext* cx, HandleValue heritage)
         return false;
     }
 
-    ReportValueError2(cx, JSMSG_BAD_HERITAGE, -1, heritage, nullptr, "not an object or null");
+    ReportValueError(cx, JSMSG_BAD_HERITAGE, -1, heritage, nullptr, "not an object or null");
     return false;
 }
 
diff --git a/js/src/vm/JSContext.cpp b/js/src/vm/JSContext.cpp
index 86d01b7778cc..f0557f4b59b6 100644
--- a/js/src/vm/JSContext.cpp
+++ b/js/src/vm/JSContext.cpp
@@ -895,36 +895,26 @@ js::ReportIsNotDefined(JSContext* cx, HandlePropertyName name)
     ReportIsNotDefined(cx, id);
 }
 
-bool
-js::ReportIsNullOrUndefined(JSContext* cx, int spindex, HandleValue v,
-                            HandleString fallback)
+void
+js::ReportIsNullOrUndefined(JSContext* cx, int spindex, HandleValue v)
 {
-    bool ok;
+    MOZ_ASSERT(v.isNullOrUndefined());
 
-    UniqueChars bytes = DecompileValueGenerator(cx, spindex, v, fallback);
+    UniqueChars bytes = DecompileValueGenerator(cx, spindex, v, nullptr);
     if (!bytes)
-        return false;
+        return;
 
-    if (strcmp(bytes.get(), js_undefined_str) == 0 ||
-        strcmp(bytes.get(), js_null_str) == 0) {
-        ok = JS_ReportErrorFlagsAndNumberLatin1(cx, JSREPORT_ERROR,
-                                                GetErrorMessage, nullptr,
-                                                JSMSG_NO_PROPERTIES,
-                                                bytes.get());
+    if (strcmp(bytes.get(), js_undefined_str) == 0 || strcmp(bytes.get(), js_null_str) == 0) {
+        JS_ReportErrorNumberLatin1(cx, GetErrorMessage, nullptr, JSMSG_NO_PROPERTIES,
+                                   bytes.get());
     } else if (v.isUndefined()) {
-        ok = JS_ReportErrorFlagsAndNumberLatin1(cx, JSREPORT_ERROR,
-                                                GetErrorMessage, nullptr,
-                                                JSMSG_UNEXPECTED_TYPE,
-                                                bytes.get(), js_undefined_str);
+        JS_ReportErrorNumberLatin1(cx, GetErrorMessage, nullptr, JSMSG_UNEXPECTED_TYPE,
+                                   bytes.get(), js_undefined_str);
     } else {
         MOZ_ASSERT(v.isNull());
-        ok = JS_ReportErrorFlagsAndNumberLatin1(cx, JSREPORT_ERROR,
-                                                GetErrorMessage, nullptr,
-                                                JSMSG_UNEXPECTED_TYPE,
-                                                bytes.get(), js_null_str);
+        JS_ReportErrorNumberLatin1(cx, GetErrorMessage, nullptr, JSMSG_UNEXPECTED_TYPE,
+                                   bytes.get(), js_null_str);
     }
-
-    return ok;
 }
 
 void
@@ -950,18 +940,14 @@ js::ReportValueErrorFlags(JSContext* cx, unsigned flags, const unsigned errorNum
                           int spindex, HandleValue v, HandleString fallback,
                           const char* arg1, const char* arg2)
 {
-    UniqueChars bytes;
-    bool ok;
-
     MOZ_ASSERT(js_ErrorFormatString[errorNumber].argCount >= 1);
     MOZ_ASSERT(js_ErrorFormatString[errorNumber].argCount <= 3);
-    bytes = DecompileValueGenerator(cx, spindex, v, fallback);
+    UniqueChars bytes = DecompileValueGenerator(cx, spindex, v, fallback);
     if (!bytes)
         return false;
 
-    ok = JS_ReportErrorFlagsAndNumberLatin1(cx, flags, GetErrorMessage, nullptr, errorNumber,
-                                            bytes.get(), arg1, arg2);
-    return ok;
+    return JS_ReportErrorFlagsAndNumberLatin1(cx, flags, GetErrorMessage, nullptr, errorNumber,
+                                              bytes.get(), arg1, arg2);
 }
 
 JSObject*
diff --git a/js/src/vm/JSContext.h b/js/src/vm/JSContext.h
index 8980f5153e46..c760857d7961 100644
--- a/js/src/vm/JSContext.h
+++ b/js/src/vm/JSContext.h
@@ -1015,8 +1015,8 @@ ReportIsNotDefined(JSContext* cx, HandleId id);
 /*
  * Report an attempt to access the property of a null or undefined value (v).
  */
-extern bool
-ReportIsNullOrUndefined(JSContext* cx, int spindex, HandleValue v, HandleString fallback);
+extern void
+ReportIsNullOrUndefined(JSContext* cx, int spindex, HandleValue v);
 
 extern void
 ReportMissingArg(JSContext* cx, js::HandleValue v, unsigned arg);
@@ -1031,17 +1031,12 @@ ReportValueErrorFlags(JSContext* cx, unsigned flags, const unsigned errorNumber,
                       int spindex, HandleValue v, HandleString fallback,
                       const char* arg1, const char* arg2);
 
-#define ReportValueError(cx,errorNumber,spindex,v,fallback)                   \
-    ((void)ReportValueErrorFlags(cx, JSREPORT_ERROR, errorNumber,             \
-                                    spindex, v, fallback, nullptr, nullptr))
-
-#define ReportValueError2(cx,errorNumber,spindex,v,fallback,arg1)             \
-    ((void)ReportValueErrorFlags(cx, JSREPORT_ERROR, errorNumber,             \
-                                    spindex, v, fallback, arg1, nullptr))
-
-#define ReportValueError3(cx,errorNumber,spindex,v,fallback,arg1,arg2)        \
-    ((void)ReportValueErrorFlags(cx, JSREPORT_ERROR, errorNumber,             \
-                                    spindex, v, fallback, arg1, arg2))
+inline void
+ReportValueError(JSContext* cx, const unsigned errorNumber, int spindex, HandleValue v,
+                 HandleString fallback, const char* arg1 = nullptr, const char* arg2 = nullptr)
+{
+    ReportValueErrorFlags(cx, JSREPORT_ERROR, errorNumber, spindex, v, fallback, arg1, arg2);
+}
 
 JSObject*
 CreateErrorNotesArray(JSContext* cx, JSErrorReport* report);
diff --git a/js/src/vm/JSFunction.cpp b/js/src/vm/JSFunction.cpp
index d3c966460bb9..cbe6aff718a3 100644
--- a/js/src/vm/JSFunction.cpp
+++ b/js/src/vm/JSFunction.cpp
@@ -116,8 +116,7 @@ AdvanceToActiveCallLinear(JSContext* cx, NonBuiltinScriptFrameIter& iter, Handle
 void
 js::ThrowTypeErrorBehavior(JSContext* cx)
 {
-    JS_ReportErrorFlagsAndNumberASCII(cx, JSREPORT_ERROR, GetErrorMessage, nullptr,
-                                     JSMSG_THROW_TYPE_ERROR);
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr, JSMSG_THROW_TYPE_ERROR);
 }
 
 static bool
@@ -311,8 +310,7 @@ CallerGetterImpl(JSContext* cx, const CallArgs& args)
         MOZ_ASSERT(!callerFun->isBuiltin(), "non-builtin iterator returned a builtin?");
 
         if (callerFun->strict()) {
-            JS_ReportErrorFlagsAndNumberASCII(cx, JSREPORT_ERROR, GetErrorMessage, nullptr,
-                                              JSMSG_CALLER_IS_STRICT);
+            JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr, JSMSG_CALLER_IS_STRICT);
             return false;
         }
     }
@@ -380,8 +378,7 @@ CallerSetterImpl(JSContext* cx, const CallArgs& args)
     MOZ_ASSERT(!callerFun->isBuiltin(), "non-builtin iterator returned a builtin?");
 
     if (callerFun->strict()) {
-        JS_ReportErrorFlagsAndNumberASCII(cx, JSREPORT_ERROR, GetErrorMessage, nullptr,
-                                          JSMSG_CALLER_IS_STRICT);
+        JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr, JSMSG_CALLER_IS_STRICT);
         return false;
     }
 
diff --git a/js/src/vm/JSObject.cpp b/js/src/vm/JSObject.cpp
index 543136f1cb1f..437092d1b979 100644
--- a/js/src/vm/JSObject.cpp
+++ b/js/src/vm/JSObject.cpp
@@ -2624,33 +2624,6 @@ js::HasOwnDataPropertyPure(JSContext* cx, JSObject* obj, jsid id, bool* result)
     return true;
 }
 
-/* static */ bool
-JSObject::reportReadOnly(JSContext* cx, jsid id, unsigned report)
-{
-    RootedValue val(cx, IdToValue(id));
-    return ReportValueErrorFlags(cx, report, JSMSG_READ_ONLY,
-                                 JSDVG_IGNORE_STACK, val, nullptr,
-                                 nullptr, nullptr);
-}
-
-/* static */ bool
-JSObject::reportNotConfigurable(JSContext* cx, jsid id, unsigned report)
-{
-    RootedValue val(cx, IdToValue(id));
-    return ReportValueErrorFlags(cx, report, JSMSG_CANT_DELETE,
-                                 JSDVG_IGNORE_STACK, val, nullptr,
-                                 nullptr, nullptr);
-}
-
-/* static */ bool
-JSObject::reportNotExtensible(JSContext* cx, HandleObject obj, unsigned report)
-{
-    RootedValue val(cx, ObjectValue(*obj));
-    return ReportValueErrorFlags(cx, report, JSMSG_OBJECT_NOT_EXTENSIBLE,
-                                 JSDVG_IGNORE_STACK, val, nullptr,
-                                 nullptr, nullptr);
-}
-
 bool
 js::GetPrototypeIfOrdinary(JSContext* cx, HandleObject obj, bool* isOrdinary,
                            MutableHandleObject protop)
@@ -3086,10 +3059,10 @@ ReportCantConvert(JSContext* cx, unsigned errorNumber, HandleObject obj, JSType
     }
 
     RootedValue val(cx, ObjectValue(*obj));
-    ReportValueError2(cx, errorNumber, JSDVG_SEARCH_STACK, val, str,
-                      hint == JSTYPE_UNDEFINED
-                      ? "primitive type"
-                      : hint == JSTYPE_STRING ? "string" : "number");
+    ReportValueError(cx, errorNumber, JSDVG_SEARCH_STACK, val, str,
+                     hint == JSTYPE_UNDEFINED
+                     ? "primitive type"
+                     : hint == JSTYPE_STRING ? "string" : "number");
     return false;
 }
 
@@ -3273,7 +3246,7 @@ js::PrimitiveToObject(JSContext* cx, const Value& v)
 
 /*
  * Invokes the ES5 ToObject algorithm on vp, returning the result. If vp might
- * already be an object, use ToObject. reportCantConvert controls how null and
+ * already be an object, use ToObject. reportScanStack controls how null and
  * undefined errors are reported.
  *
  * Callers must handle the already-object case.
@@ -3286,7 +3259,7 @@ js::ToObjectSlow(JSContext* cx, JS::HandleValue val, bool reportScanStack)
 
     if (val.isNullOrUndefined()) {
         if (reportScanStack) {
-            ReportIsNullOrUndefined(cx, JSDVG_SEARCH_STACK, val, nullptr);
+            ReportIsNullOrUndefined(cx, JSDVG_SEARCH_STACK, val);
         } else {
             JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr, JSMSG_CANT_CONVERT_TO,
                                       val.isNull() ? "null" : "undefined", "object");
diff --git a/js/src/vm/JSObject.h b/js/src/vm/JSObject.h
index 35656b424d40..d3ab5e775d66 100644
--- a/js/src/vm/JSObject.h
+++ b/js/src/vm/JSObject.h
@@ -480,11 +480,6 @@ class JSObject : public js::gc::Cell
     MOZ_ALWAYS_INLINE void finalize(js::FreeOp* fop);
 
   public:
-    static bool reportReadOnly(JSContext* cx, jsid id, unsigned report = JSREPORT_ERROR);
-    static bool reportNotConfigurable(JSContext* cx, jsid id, unsigned report = JSREPORT_ERROR);
-    static bool reportNotExtensible(JSContext* cx, js::HandleObject obj,
-                                    unsigned report = JSREPORT_ERROR);
-
     static bool nonNativeSetProperty(JSContext* cx, js::HandleObject obj, js::HandleId id,
                                      js::HandleValue v, js::HandleValue receiver,
                                      JS::ObjectOpResult& result);
diff --git a/js/src/vm/NativeObject-inl.h b/js/src/vm/NativeObject-inl.h
index 6be0b1c54937..70b9faddb0f4 100644
--- a/js/src/vm/NativeObject-inl.h
+++ b/js/src/vm/NativeObject-inl.h
@@ -967,8 +967,9 @@ ThrowIfNotConstructing(JSContext *cx, const CallArgs &args, const char *builtinN
 {
     if (args.isConstructing())
         return true;
-    return JS_ReportErrorFlagsAndNumberASCII(cx, JSREPORT_ERROR, GetErrorMessage, nullptr,
-                                             JSMSG_BUILTIN_CTOR_NO_NEW, builtinName);
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr, JSMSG_BUILTIN_CTOR_NO_NEW,
+                              builtinName);
+    return false;
 }
 
 inline bool
diff --git a/js/src/vm/NativeObject.cpp b/js/src/vm/NativeObject.cpp
index 60458e4940bb..1b41456918f4 100644
--- a/js/src/vm/NativeObject.cpp
+++ b/js/src/vm/NativeObject.cpp
@@ -1707,18 +1707,8 @@ js::NativeDefineProperty(JSContext* cx, HandleNativeObject obj, HandleId id,
         return result.succeed();
     }
 
-    // Non-standard hack: Allow redefining non-configurable properties if
-    // JSPROP_REDEFINE_NONCONFIGURABLE is set _and_ the object is a non-DOM
-    // global. The idea is that a DOM object can never have such a thing on
-    // its proto chain directly on the web, so we should be OK optimizing
-    // access to accessors found on such an object. Bug 1105518 contemplates
-    // removing this hack.
-    bool skipRedefineChecks = (desc.attributes() & JSPROP_REDEFINE_NONCONFIGURABLE) &&
-                              obj->is<GlobalObject>() &&
-                              !obj->getClass()->isDOMClass();
-
     // Step 4.
-    if (!IsConfigurable(shapeAttrs) && !skipRedefineChecks) {
+    if (!IsConfigurable(shapeAttrs)) {
         if (desc.hasConfigurable() && desc.configurable())
             return result.fail(JSMSG_CANT_REDEFINE_PROP);
         if (desc.hasEnumerable() && desc.enumerable() != IsEnumerable(shapeAttrs))
@@ -1753,7 +1743,7 @@ js::NativeDefineProperty(JSContext* cx, HandleNativeObject obj, HandleId id,
         }
     } else if (desc.isDataDescriptor() != IsDataDescriptor(shapeAttrs)) {
         // Step 6.
-        if (!IsConfigurable(shapeAttrs) && !skipRedefineChecks)
+        if (!IsConfigurable(shapeAttrs))
             return result.fail(JSMSG_CANT_REDEFINE_PROP);
 
         // Fill in desc fields with default values (steps 6.b.i and 6.c.i).
@@ -1763,7 +1753,7 @@ js::NativeDefineProperty(JSContext* cx, HandleNativeObject obj, HandleId id,
         bool frozen = !IsConfigurable(shapeAttrs) && !IsWritable(shapeAttrs);
 
         // Step 7.a.i.1.
-        if (frozen && desc.hasWritable() && desc.writable() && !skipRedefineChecks)
+        if (frozen && desc.hasWritable() && desc.writable())
             return result.fail(JSMSG_CANT_REDEFINE_PROP);
 
         if (frozen || !desc.hasValue()) {
@@ -1780,13 +1770,13 @@ js::NativeDefineProperty(JSContext* cx, HandleNativeObject obj, HandleId id,
                 MOZ_ASSERT(!cx->helperThread());
                 if (!SameValue(cx, desc.value(), currentValue, &same))
                     return false;
-                if (!same && !skipRedefineChecks)
+                if (!same)
                     return result.fail(JSMSG_CANT_REDEFINE_PROP);
             }
         }
 
         // Step 7.a.i.3.
-        if (frozen && !skipRedefineChecks)
+        if (frozen)
             return result.succeed();
 
         // Fill in desc.[[Writable]].
@@ -1802,8 +1792,7 @@ js::NativeDefineProperty(JSContext* cx, HandleNativeObject obj, HandleId id,
         if (desc.hasSetterObject()) {
             // Step 8.a.i.
             if (!IsConfigurable(shapeAttrs) &&
-                desc.setterObject() != prop.shape()->setterObject() &&
-                !skipRedefineChecks)
+                desc.setterObject() != prop.shape()->setterObject())
             {
                 return result.fail(JSMSG_CANT_REDEFINE_PROP);
             }
@@ -1814,8 +1803,7 @@ js::NativeDefineProperty(JSContext* cx, HandleNativeObject obj, HandleId id,
         if (desc.hasGetterObject()) {
             // Step 8.a.ii.
             if (!IsConfigurable(shapeAttrs) &&
-                desc.getterObject() != prop.shape()->getterObject() &&
-                !skipRedefineChecks)
+                desc.getterObject() != prop.shape()->getterObject())
             {
                 return result.fail(JSMSG_CANT_REDEFINE_PROP);
             }
diff --git a/js/src/vm/RegExpObject.cpp b/js/src/vm/RegExpObject.cpp
index eba1c05e47b6..68b30b19453a 100644
--- a/js/src/vm/RegExpObject.cpp
+++ b/js/src/vm/RegExpObject.cpp
@@ -1423,8 +1423,7 @@ js::ParseRegExpFlags(JSContext* cx, JSString* flagStr, RegExpFlag* flagsOut)
         UniqueChars utf8(JS::CharsToNewUTF8CharsZ(nullptr, range).c_str());
         if (!utf8)
             return false;
-        JS_ReportErrorFlagsAndNumberUTF8(cx, JSREPORT_ERROR, GetErrorMessage, nullptr,
-                                         JSMSG_BAD_REGEXP_FLAG, utf8.get());
+        JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr, JSMSG_BAD_REGEXP_FLAG, utf8.get());
         return false;
     }
 
diff --git a/js/src/vm/SelfHosting.cpp b/js/src/vm/SelfHosting.cpp
index 5fb2ae435327..02ad7bea7ad4 100644
--- a/js/src/vm/SelfHosting.cpp
+++ b/js/src/vm/SelfHosting.cpp
@@ -2906,8 +2906,8 @@ VerifyGlobalNames(JSContext* cx, Handle<GlobalObject*> shg)
 
     if (nameMissing) {
         RootedValue value(cx, IdToValue(id));
-        return ReportValueErrorFlags(cx, JSREPORT_ERROR, JSMSG_NO_SUCH_SELF_HOSTED_PROP,
-                                     JSDVG_IGNORE_STACK, value, nullptr, nullptr, nullptr);
+        ReportValueError(cx, JSMSG_NO_SUCH_SELF_HOSTED_PROP, JSDVG_IGNORE_STACK, value, nullptr);
+        return false;
     }
 #endif // DEBUG
 
diff --git a/layout/painting/DisplayItemClipChain.h b/layout/painting/DisplayItemClipChain.h
index 532c52e1729f..413b8d8c1d60 100644
--- a/layout/painting/DisplayItemClipChain.h
+++ b/layout/painting/DisplayItemClipChain.h
@@ -72,8 +72,9 @@ struct DisplayItemClipChain {
   {}
 
   DisplayItemClipChain()
+    : mASR(nullptr)
 #ifdef DEBUG
-    : mOnStack(true)
+    , mOnStack(true)
 #endif
   {}
 
diff --git a/layout/painting/DottedCornerFinder.cpp b/layout/painting/DottedCornerFinder.cpp
index e3d020e4556b..9c41ac2bb532 100644
--- a/layout/painting/DottedCornerFinder.cpp
+++ b/layout/painting/DottedCornerFinder.cpp
@@ -57,7 +57,7 @@ DottedCornerFinder::DottedCornerFinder(const Bezier& aOuterBezier,
    mNormalSign((aCorner == C_TL || aCorner == C_BR) ? -1.0f : 1.0f),
    mC0(aC0), mCn(aCn),
    mR0(aR0), mRn(aRn), mMaxR(std::max(aR0, aRn)),
-   mCenterCurveOrigin(mC0.x, mCn.y),
+   mCenterCurveOrigin(mC0.x, mCn.y), mCenterCurveR(0.0),
    mInnerCurveOrigin(mInnerBezier.mPoints[0].x, mInnerBezier.mPoints[3].y),
    mBestOverlap(0.0f),
    mHasZeroBorderWidth(false), mHasMore(true),
diff --git a/layout/painting/FrameLayerBuilder.cpp b/layout/painting/FrameLayerBuilder.cpp
index 2e8f1dd70601..1fbb84429842 100644
--- a/layout/painting/FrameLayerBuilder.cpp
+++ b/layout/painting/FrameLayerBuilder.cpp
@@ -533,6 +533,7 @@ public:
   PaintedLayerData() :
     mAnimatedGeometryRoot(nullptr),
     mASR(nullptr),
+    mClipChain(nullptr),
     mReferenceFrame(nullptr),
     mLayer(nullptr),
     mSolidColor(NS_RGBA(0, 0, 0, 0)),
@@ -1637,7 +1638,8 @@ public:
     mAnimatedGeometryRootPosition(0, 0),
     mLastItemCount(0),
     mContainerLayerFrame(nullptr),
-    mHasExplicitLastPaintOffset(false) {}
+    mHasExplicitLastPaintOffset(false),
+    mDisabledAlpha(false) {}
 
   NS_INLINE_DECL_REFCOUNTING(PaintedDisplayItemLayerUserData);
 
@@ -1725,6 +1727,7 @@ protected:
 
 FrameLayerBuilder::FrameLayerBuilder()
   : mRetainingManager(nullptr)
+  , mDisplayListBuilder(nullptr)
   , mContainingPaintedLayer(nullptr)
   , mInactiveLayerClip(nullptr)
   , mInvalidateAllLayers(false)
diff --git a/layout/painting/nsCSSRendering.cpp b/layout/painting/nsCSSRendering.cpp
index 6022a97c3ff7..1fe5eff1d053 100644
--- a/layout/painting/nsCSSRendering.cpp
+++ b/layout/painting/nsCSSRendering.cpp
@@ -77,7 +77,10 @@ static int gFrameTreeLockCount = 0;
 struct InlineBackgroundData
 {
   InlineBackgroundData()
-      : mFrame(nullptr), mLineContainer(nullptr)
+      : mFrame(nullptr), mLineContainer(nullptr),
+        mContinuationPoint(0), mUnbrokenMeasure(0), 
+        mLineContinuationPoint(0), mPIStartBorderData{},
+        mBidiEnabled(false), mVertical(false)
   {
   }
 
diff --git a/layout/painting/nsCSSRenderingGradients.h b/layout/painting/nsCSSRenderingGradients.h
index 9c477ae7ad7e..7fecbb5dc2f6 100644
--- a/layout/painting/nsCSSRenderingGradients.h
+++ b/layout/painting/nsCSSRenderingGradients.h
@@ -91,7 +91,12 @@ public:
                                   float aOpacity = 1.0);
 
 private:
-  nsCSSGradientRenderer() {}
+  nsCSSGradientRenderer()
+    : mPresContext(nullptr)
+    , mGradient(nullptr)
+    , mRadiusX(0.0)
+    , mRadiusY(0.0)
+  {}
 
   /**
    * Attempts to paint the tiles for a gradient by painting it once to an
diff --git a/layout/painting/nsDisplayList.h b/layout/painting/nsDisplayList.h
index 002a87af5d20..c839ceb98fea 100644
--- a/layout/painting/nsDisplayList.h
+++ b/layout/painting/nsDisplayList.h
@@ -323,6 +323,9 @@ struct ActiveScrolledRoot {
 
 private:
   ActiveScrolledRoot()
+    : mScrollableFrame(nullptr)
+    , mDepth(0)
+    , mRetained(false)
   {
   }
 
diff --git a/layout/painting/nsImageRenderer.h b/layout/painting/nsImageRenderer.h
index e73ff231977e..57bb0a8f2d0f 100644
--- a/layout/painting/nsImageRenderer.h
+++ b/layout/painting/nsImageRenderer.h
@@ -33,8 +33,11 @@ struct CSSSizeOrRatio
 {
   CSSSizeOrRatio()
     : mRatio(0, 0)
+    , mWidth(0)
+    , mHeight(0)
     , mHasWidth(false)
-    , mHasHeight(false) {}
+    , mHasHeight(false)
+  {}
 
   bool CanComputeConcreteSize() const
   {
diff --git a/layout/svg/SVGContextPaint.h b/layout/svg/SVGContextPaint.h
index 9beba95adb68..277d67df5537 100644
--- a/layout/svg/SVGContextPaint.h
+++ b/layout/svg/SVGContextPaint.h
@@ -190,7 +190,10 @@ public:
   float GetStrokeOpacity() const override { return mStrokeOpacity; }
 
   struct Paint {
-    Paint() : mPaintType(eStyleSVGPaintType_None) {}
+    Paint()
+      : mPaintDefinition{}
+      , mPaintType(eStyleSVGPaintType_None)
+    {}
 
     void SetPaintServer(nsIFrame* aFrame,
                         const gfxMatrix& aContextMatrix,
diff --git a/layout/svg/SVGTextFrame.cpp b/layout/svg/SVGTextFrame.cpp
index 8aaafcfae26c..f75fbc24867b 100644
--- a/layout/svg/SVGTextFrame.cpp
+++ b/layout/svg/SVGTextFrame.cpp
@@ -2439,10 +2439,12 @@ CharIterator::CharIterator(SVGTextFrame* aSVGTextFrame,
     mFrameForTrimCheck(nullptr),
     mTrimmedOffset(0),
     mTrimmedLength(0),
+    mTextRun(nullptr),
     mTextElementCharIndex(0),
     mGlyphStartTextElementCharIndex(0),
-    mLengthAdjustScaleFactor(aSVGTextFrame->mLengthAdjustScaleFactor)
-  , mPostReflow(aPostReflow)
+    mGlyphUndisplayedCharacters(0),
+    mLengthAdjustScaleFactor(aSVGTextFrame->mLengthAdjustScaleFactor),
+    mPostReflow(aPostReflow)
 {
   if (!AtEnd()) {
     mSkipCharsIterator = TextFrame()->EnsureTextRun(nsTextFrame::eInflated);
@@ -2772,7 +2774,8 @@ public:
       mContext(aContext),
       mFrame(aFrame),
       mCanvasTM(aCanvasTM),
-      mImgParams(aImgParams)
+      mImgParams(aImgParams),
+      mColor(0)
   {
   }