diff --git a/dom/base/nsWrapperCache.cpp b/dom/base/nsWrapperCache.cpp
index 7ad24df3edb1..0b19e1a3630f 100644
--- a/dom/base/nsWrapperCache.cpp
+++ b/dom/base/nsWrapperCache.cpp
@@ -102,7 +102,7 @@ DebugWrapperTraceCallback(JS::GCCellPtr aPtr, const char* aName, void* aClosure)
   DebugWrapperTraversalCallback* callback =
     static_cast<DebugWrapperTraversalCallback*>(aClosure);
   if (aPtr.is<JSObject>()) {
-    callback->NoteJSObject(&aPtr.to<JSObject>());
+    callback->NoteJSObject(&aPtr.as<JSObject>());
   }
 }
 
diff --git a/dom/xbl/nsXBLDocumentInfo.cpp b/dom/xbl/nsXBLDocumentInfo.cpp
index 4c3e19bdd6dc..6c7f834c8462 100644
--- a/dom/xbl/nsXBLDocumentInfo.cpp
+++ b/dom/xbl/nsXBLDocumentInfo.cpp
@@ -77,7 +77,7 @@ NS_IMPL_CYCLE_COLLECTION_TRACE_END
 static void
 UnmarkXBLJSObject(JS::GCCellPtr aPtr, const char* aName, void* aClosure)
 {
-  JS::ExposeObjectToActiveJS(&aPtr.to<JSObject>());
+  JS::ExposeObjectToActiveJS(&aPtr.as<JSObject>());
 }
 
 static PLDHashOperator
diff --git a/js/public/HeapAPI.h b/js/public/HeapAPI.h
index 9028e847a445..57c05b30fdf2 100644
--- a/js/public/HeapAPI.h
+++ b/js/public/HeapAPI.h
@@ -164,8 +164,8 @@ class JS_FRIEND_API(GCCellPtr)
 
     // Construction from an explicit type.
     template <typename T>
-    explicit GCCellPtr(T* ptr) : ptr(checkedCast(ptr, JS::MapTypeToTraceKind<T>::kind)) { }
-    explicit GCCellPtr(JSFunction* ptr) : ptr(checkedCast(ptr, JS::TraceKind::Object)) { }
+    explicit GCCellPtr(T* p) : ptr(checkedCast(p, JS::MapTypeToTraceKind<T>::kind)) { }
+    explicit GCCellPtr(JSFunction* p) : ptr(checkedCast(p, JS::TraceKind::Object)) { }
     explicit GCCellPtr(JSFlatString* str) : ptr(checkedCast(str, JS::TraceKind::String)) { }
     explicit GCCellPtr(const Value& v);
 
@@ -189,7 +189,7 @@ class JS_FRIEND_API(GCCellPtr)
     // Conversions to more specific types must match the kind. Access to
     // further refined types is not allowed directly from a GCCellPtr.
     template <typename T>
-    T& to() const {
+    T& as() const {
         MOZ_ASSERT(kind() == JS::MapTypeToTraceKind<T>::kind);
         // We can't use static_cast here, because the fact that JSObject
         // inherits from js::gc::Cell is not part of the public API.
diff --git a/js/src/gc/Tracer.cpp b/js/src/gc/Tracer.cpp
index cf34ab9fa21d..ae4c8b3aef84 100644
--- a/js/src/gc/Tracer.cpp
+++ b/js/src/gc/Tracer.cpp
@@ -341,7 +341,7 @@ ObjectGroupCycleCollectorTracer::onChild(const JS::GCCellPtr& thing)
     if (thing.is<ObjectGroup>()) {
         // If this group is required to be in an ObjectGroup chain, trace it
         // via the provided worklist rather than continuing to recurse.
-        ObjectGroup& group = thing.to<ObjectGroup>();
+        ObjectGroup& group = thing.as<ObjectGroup>();
         if (group.maybeUnboxedLayout()) {
             for (size_t i = 0; i < seen.length(); i++) {
                 if (seen[i] == &group)
diff --git a/js/src/gdb/mozilla/Root.py b/js/src/gdb/mozilla/Root.py
index b60d49abea38..c93590731aca 100644
--- a/js/src/gdb/mozilla/Root.py
+++ b/js/src/gdb/mozilla/Root.py
@@ -18,6 +18,10 @@ class Common(object):
     # the template member holds the referent directly.
     handle = False
 
+    # If True, we should strip typedefs from our referent type. (Rooted<T>
+    # uses template magic that gives the referent a noisy type.)
+    strip_typedefs = False
+
     # Initialize a pretty-printer for |value|, using |cache|.
     #
     # If given, |content_printer| is a pretty-printer constructor to use for
@@ -42,6 +46,8 @@ class Common(object):
         ptr = self.value[self.member]
         if self.handle:
             ptr = ptr.dereference()
+        if self.strip_typedefs:
+            ptr = ptr.cast(ptr.type.strip_typedefs())
         if self.content_printer:
             return self.content_printer(ptr, self.cache).to_string()
         else:
@@ -53,7 +59,7 @@ class Common(object):
 
 @template_pretty_printer("JS::Rooted")
 class Rooted(Common):
-    pass
+    strip_typedefs = True
 
 @template_pretty_printer("JS::Handle")
 class Handle(Common):
diff --git a/js/src/jsfriendapi.cpp b/js/src/jsfriendapi.cpp
index 05f0d4535256..5d39a43980fa 100644
--- a/js/src/jsfriendapi.cpp
+++ b/js/src/jsfriendapi.cpp
@@ -206,14 +206,14 @@ JS_FRIEND_API(void)
 JS_TraceShapeCycleCollectorChildren(JS::CallbackTracer* trc, JS::GCCellPtr shape)
 {
     MOZ_ASSERT(shape.is<Shape>());
-    TraceCycleCollectorChildren(trc, &shape.to<Shape>());
+    TraceCycleCollectorChildren(trc, &shape.as<Shape>());
 }
 
 JS_FRIEND_API(void)
 JS_TraceObjectGroupCycleCollectorChildren(JS::CallbackTracer* trc, JS::GCCellPtr group)
 {
     MOZ_ASSERT(group.is<ObjectGroup>());
-    TraceCycleCollectorChildren(trc, &group.to<ObjectGroup>());
+    TraceCycleCollectorChildren(trc, &group.as<ObjectGroup>());
 }
 
 static bool
@@ -853,7 +853,7 @@ struct DumpHeapTracer : public JS::CallbackTracer, public WeakMapTracer
     void trace(JSObject* map, JS::GCCellPtr key, JS::GCCellPtr value) override {
         JSObject* kdelegate = nullptr;
         if (key.is<JSObject>())
-            kdelegate = js::GetWeakmapKeyDelegate(&key.to<JSObject>());
+            kdelegate = js::GetWeakmapKeyDelegate(&key.as<JSObject>());
 
         fprintf(output, "WeakMapEntry map=%p key=%p keyDelegate=%p value=%p\n",
                 map, key.asCell(), kdelegate, value.asCell());
diff --git a/js/src/jsgc.cpp b/js/src/jsgc.cpp
index 8db886091105..d5d4f5654dbe 100644
--- a/js/src/jsgc.cpp
+++ b/js/src/jsgc.cpp
@@ -7003,8 +7003,8 @@ JS::GCCellPtr::outOfLineKind() const
 bool
 JS::GCCellPtr::mayBeOwnedByOtherRuntime() const
 {
-    return (is<JSString>() && to<JSString>().isPermanentAtom()) ||
-           (is<Symbol>() && to<Symbol>().isWellKnownSymbol());
+    return (is<JSString>() && as<JSString>().isPermanentAtom()) ||
+           (is<Symbol>() && as<Symbol>().isWellKnownSymbol());
 }
 
 #ifdef JSGC_HASH_TABLE_CHECKS
diff --git a/js/src/vm/UbiNode.cpp b/js/src/vm/UbiNode.cpp
index d78cf7bc4883..5bd529a0a512 100644
--- a/js/src/vm/UbiNode.cpp
+++ b/js/src/vm/UbiNode.cpp
@@ -118,9 +118,9 @@ class SimpleEdgeVectorTracer : public JS::CallbackTracer {
 
         // Don't trace permanent atoms and well-known symbols that are owned by
         // a parent JSRuntime.
-        if (thing.is<JSString>() && thing.to<JSString>().isPermanentAtom())
+        if (thing.is<JSString>() && thing.as<JSString>().isPermanentAtom())
             return;
-        if (thing.is<JS::Symbol>() && thing.to<JS::Symbol>().isWellKnownSymbol())
+        if (thing.is<JS::Symbol>() && thing.as<JS::Symbol>().isWellKnownSymbol())
             return;
 
         char16_t* name16 = nullptr;
diff --git a/xpcom/base/CycleCollectedJSRuntime.cpp b/xpcom/base/CycleCollectedJSRuntime.cpp
index 6ec7c371a75b..d8ec1b44ba68 100644
--- a/xpcom/base/CycleCollectedJSRuntime.cpp
+++ b/xpcom/base/CycleCollectedJSRuntime.cpp
@@ -189,7 +189,7 @@ NoteWeakMapsTracer::trace(JSObject* aMap, JS::GCCellPtr aKey,
 
   JSObject* kdelegate = nullptr;
   if (aKey.is<JSObject>()) {
-    kdelegate = js::GetWeakmapKeyDelegate(&aKey.to<JSObject>());
+    kdelegate = js::GetWeakmapKeyDelegate(&aKey.as<JSObject>());
   }
 
   if (AddToCCKind(aValue.kind())) {
@@ -245,7 +245,7 @@ struct FixWeakMappingGrayBitsTracer : public js::WeakMapTracer
     }
 
     if (delegateMightNeedMarking && aKey.is<JSObject>()) {
-      JSObject* kdelegate = js::GetWeakmapKeyDelegate(&aKey.to<JSObject>());
+      JSObject* kdelegate = js::GetWeakmapKeyDelegate(&aKey.as<JSObject>());
       if (kdelegate && !JS::ObjectIsMarkedGray(kdelegate)) {
         if (JS::UnmarkGrayGCThingRecursively(aKey)) {
           mAnyMarked = true;
@@ -344,9 +344,9 @@ TraversalTracer::onChild(const JS::GCCellPtr& aThing)
       mCb.NoteNextEdgeName(buffer);
     }
     if (aThing.is<JSObject>()) {
-      mCb.NoteJSObject(&aThing.to<JSObject>());
+      mCb.NoteJSObject(&aThing.as<JSObject>());
     } else {
-      mCb.NoteJSScript(&aThing.to<JSScript>());
+      mCb.NoteJSScript(&aThing.as<JSScript>());
     }
   } else if (aThing.is<js::Shape>()) {
     // The maximum depth of traversal when tracing a Shape is unbounded, due to
@@ -484,7 +484,7 @@ CycleCollectedJSRuntime::DescribeGCThing(bool aIsMarked, JS::GCCellPtr aThing,
   char name[72];
   uint64_t compartmentAddress = 0;
   if (aThing.is<JSObject>()) {
-    JSObject* obj = &aThing.to<JSObject>();
+    JSObject* obj = &aThing.as<JSObject>();
     compartmentAddress = (uint64_t)js::GetObjectCompartment(obj);
     const js::Class* clasp = js::GetObjectClass(obj);
 
@@ -583,7 +583,7 @@ CycleCollectedJSRuntime::TraverseGCThing(TraverseSelect aTs, JS::GCCellPtr aThin
   }
 
   if (aThing.is<JSObject>()) {
-    JSObject* obj = &aThing.to<JSObject>();
+    JSObject* obj = &aThing.as<JSObject>();
     NoteGCThingXPCOMChildren(js::GetObjectClass(obj), obj, aCb);
   }
 }
diff --git a/xpcom/glue/nsCycleCollectionParticipant.cpp b/xpcom/glue/nsCycleCollectionParticipant.cpp
index d080d5674eb5..ec452e9b013d 100644
--- a/xpcom/glue/nsCycleCollectionParticipant.cpp
+++ b/xpcom/glue/nsCycleCollectionParticipant.cpp
@@ -24,9 +24,9 @@ nsScriptObjectTracer::NoteJSChild(JS::GCCellPtr aGCThing, const char* aName,
     static_cast<nsCycleCollectionTraversalCallback*>(aClosure);
   NS_CYCLE_COLLECTION_NOTE_EDGE_NAME(*cb, aName);
   if (aGCThing.is<JSObject>()) {
-    cb->NoteJSObject(&aGCThing.to<JSObject>());
+    cb->NoteJSObject(&aGCThing.as<JSObject>());
   } else if (aGCThing.is<JSScript>()) {
-    cb->NoteJSScript(&aGCThing.to<JSScript>());
+    cb->NoteJSScript(&aGCThing.as<JSScript>());
   } else {
     MOZ_ASSERT(!mozilla::AddToCCKind(aGCThing.kind()));
   }