diff --git a/dom/base/nsDOMWindowUtils.cpp b/dom/base/nsDOMWindowUtils.cpp
index b662b230cbdc..f84e934d9c2e 100644
--- a/dom/base/nsDOMWindowUtils.cpp
+++ b/dom/base/nsDOMWindowUtils.cpp
@@ -816,7 +816,7 @@ nsDOMWindowUtils::GarbageCollect(nsICycleCollectorListener *aListener)
   }
 #endif
 
-  nsJSContext::GarbageCollectNow();
+  nsJSContext::GarbageCollectNow(js::gcreason::DOM_UTILS);
   nsJSContext::CycleCollectNow(aListener);
 
   return NS_OK;
diff --git a/dom/base/nsGlobalWindow.cpp b/dom/base/nsGlobalWindow.cpp
index cb166608436f..76b9d3f0975b 100644
--- a/dom/base/nsGlobalWindow.cpp
+++ b/dom/base/nsGlobalWindow.cpp
@@ -2272,7 +2272,7 @@ nsGlobalWindow::SetNewDocument(nsIDocument* aDocument,
     newInnerWindow->mChromeEventHandler = mChromeEventHandler;
   }
 
-  mContext->GC();
+  mContext->GC(js::gcreason::SET_NEW_DOCUMENT);
   mContext->DidInitializeContext();
 
   if (newInnerWindow && !newInnerWindow->mHasNotifiedGlobalCreated && mDoc) {
@@ -2429,7 +2429,7 @@ nsGlobalWindow::SetDocShell(nsIDocShell* aDocShell)
     }
 
     if (mContext) {
-      mContext->GC();
+      mContext->GC(js::gcreason::SET_DOC_SHELL);
       mContext->FinalizeContext();
       mContext = nsnull;
     }
diff --git a/dom/base/nsIScriptContext.h b/dom/base/nsIScriptContext.h
index 6b16b0702dc8..c235ede9dddf 100644
--- a/dom/base/nsIScriptContext.h
+++ b/dom/base/nsIScriptContext.h
@@ -43,6 +43,7 @@
 #include "nsISupports.h"
 #include "nsCOMPtr.h"
 #include "nsIProgrammingLanguage.h"
+#include "jsfriendapi.h"
 #include "jspubtd.h"
 
 class nsIScriptGlobalObject;
@@ -354,7 +355,7 @@ public:
    *
    * @return NS_OK if the method is successful
    */
-  virtual void GC() = 0;
+  virtual void GC(js::gcreason::Reason aReason) = 0;
 
   /**
    * Inform the context that a script was evaluated.
diff --git a/dom/base/nsJSEnvironment.cpp b/dom/base/nsJSEnvironment.cpp
index 43e16b117ac1..971fa58ebbf8 100644
--- a/dom/base/nsJSEnvironment.cpp
+++ b/dom/base/nsJSEnvironment.cpp
@@ -203,7 +203,7 @@ nsMemoryPressureObserver::Observe(nsISupports* aSubject, const char* aTopic,
                                   const PRUnichar* aData)
 {
   if (sGCOnMemoryPressure) {
-    nsJSContext::GarbageCollectNow(true);
+    nsJSContext::GarbageCollectNow(js::gcreason::MEM_PRESSURE, nsGCShrinking);
     nsJSContext::CycleCollectNow();
   }
   return NS_OK;
@@ -1111,7 +1111,7 @@ nsJSContext::DestroyJSContext()
                                   js_options_dot_str, this);
 
   if (mGCOnDestruction) {
-    PokeGC();
+    PokeGC(js::gcreason::NSJSCONTEXT_DESTROY);
   }
         
   // Let xpconnect destroy the JSContext when it thinks the time is right.
@@ -3220,7 +3220,7 @@ nsJSContext::ScriptExecuted()
 
 //static
 void
-nsJSContext::GarbageCollectNow(bool shrinkingGC)
+nsJSContext::GarbageCollectNow(js::gcreason::Reason reason, PRUint32 gckind)
 {
   NS_TIME_FUNCTION_MIN(1.0);
   SAMPLE_LABEL("GC", "GarbageCollectNow");
@@ -3238,7 +3238,7 @@ nsJSContext::GarbageCollectNow(bool shrinkingGC)
   sLoadingInProgress = false;
 
   if (nsContentUtils::XPConnect()) {
-    nsContentUtils::XPConnect()->GarbageCollect(shrinkingGC);
+    nsContentUtils::XPConnect()->GarbageCollect(reason, gckind);
   }
 }
 
@@ -3276,7 +3276,7 @@ nsJSContext::CycleCollectNow(nsICycleCollectorListener *aListener)
   // If we collected a substantial amount of cycles, poke the GC since more objects
   // might be unreachable now.
   if (sCCollectedWaitingForGC > 250) {
-    PokeGC();
+    PokeGC(js::gcreason::CC_WAITING);
   }
 
   PRTime now = PR_Now();
@@ -3315,7 +3315,8 @@ GCTimerFired(nsITimer *aTimer, void *aClosure)
 {
   NS_RELEASE(sGCTimer);
 
-  nsJSContext::GarbageCollectNow();
+  uintptr_t reason = reinterpret_cast<uintptr_t>(aClosure);
+  nsJSContext::GarbageCollectNow(static_cast<js::gcreason::Reason>(reason), nsGCNormal);
 }
 
 void
@@ -3359,12 +3360,12 @@ nsJSContext::LoadEnd()
 
   // Its probably a good idea to GC soon since we have finished loading.
   sLoadingInProgress = false;
-  PokeGC();
+  PokeGC(js::gcreason::LOAD_END);
 }
 
 // static
 void
-nsJSContext::PokeGC()
+nsJSContext::PokeGC(js::gcreason::Reason aReason)
 {
   if (sGCTimer) {
     // There's already a timer for GC'ing, just return
@@ -3380,7 +3381,7 @@ nsJSContext::PokeGC()
 
   static bool first = true;
 
-  sGCTimer->InitWithFuncCallback(GCTimerFired, nsnull,
+  sGCTimer->InitWithFuncCallback(GCTimerFired, reinterpret_cast<void *>(aReason),
                                  first
                                  ? NS_FIRST_GC_DELAY
                                  : NS_GC_DELAY,
@@ -3473,9 +3474,9 @@ nsJSContext::KillCCTimer()
 }
 
 void
-nsJSContext::GC()
+nsJSContext::GC(js::gcreason::Reason aReason)
 {
-  PokeGC();
+  PokeGC(aReason);
 }
 
 static void
@@ -3513,7 +3514,7 @@ DOMGCFinishedCallback(JSRuntime *rt, JSCompartment *comp, const char *status)
     // probably a time of heavy activity and we want to delay
     // the full GC, but we do want it to happen eventually.
     if (comp) {
-      nsJSContext::PokeGC();
+      nsJSContext::PokeGC(js::gcreason::POST_COMPARTMENT);
 
       // We poked the GC, so we can kill any pending CC here.
       nsJSContext::KillCCTimer();
diff --git a/dom/base/nsJSEnvironment.h b/dom/base/nsJSEnvironment.h
index 3f43bff80406..8deda4b3545a 100644
--- a/dom/base/nsJSEnvironment.h
+++ b/dom/base/nsJSEnvironment.h
@@ -41,10 +41,12 @@
 #include "nsIScriptRuntime.h"
 #include "nsCOMPtr.h"
 #include "jsapi.h"
+#include "jsfriendapi.h"
 #include "nsIObserver.h"
 #include "nsIXPCScriptNotify.h"
 #include "prtime.h"
 #include "nsCycleCollectionParticipant.h"
+#include "nsIXPConnect.h"
 
 class nsIXPConnectJSObjectHolder;
 class nsRootedJSValueArray;
@@ -179,11 +181,11 @@ public:
   static void LoadStart();
   static void LoadEnd();
 
-  static void GarbageCollectNow(bool shrinkingGC = false);
+  static void GarbageCollectNow(js::gcreason::Reason reason, PRUint32 gckind = nsGCNormal);
   static void ShrinkGCBuffersNow();
   static void CycleCollectNow(nsICycleCollectorListener *aListener = nsnull);
 
-  static void PokeGC();
+  static void PokeGC(js::gcreason::Reason aReason);
   static void KillGCTimer();
 
   static void PokeShrinkGCBuffers();
@@ -193,7 +195,7 @@ public:
   static void MaybePokeCC();
   static void KillCCTimer();
 
-  virtual void GC();
+  virtual void GC(js::gcreason::Reason aReason);
 
 protected:
   nsresult InitializeExternalClasses();
diff --git a/dom/ipc/ContentChild.cpp b/dom/ipc/ContentChild.cpp
index 5494908162eb..c81f30fd0545 100644
--- a/dom/ipc/ContentChild.cpp
+++ b/dom/ipc/ContentChild.cpp
@@ -800,14 +800,14 @@ ContentChild::GetIndexedDBPath()
 bool
 ContentChild::RecvGarbageCollect()
 {
-    nsJSContext::GarbageCollectNow();
+    nsJSContext::GarbageCollectNow(js::gcreason::DOM_IPC);
     return true;
 }
 
 bool
 ContentChild::RecvCycleCollect()
 {
-    nsJSContext::GarbageCollectNow();
+    nsJSContext::GarbageCollectNow(js::gcreason::DOM_IPC);
     nsJSContext::CycleCollectNow();
     return true;
 }
diff --git a/dom/workers/WorkerPrivate.cpp b/dom/workers/WorkerPrivate.cpp
index d5cf0279ca5e..10b2bce6acef 100644
--- a/dom/workers/WorkerPrivate.cpp
+++ b/dom/workers/WorkerPrivate.cpp
@@ -3794,10 +3794,10 @@ WorkerPrivate::GarbageCollectInternal(JSContext* aCx, bool aShrinking,
   AssertIsOnWorkerThread();
 
   if (aShrinking) {
-    JS_ShrinkingGC(aCx);
+    js::ShrinkingGC(aCx, js::gcreason::DOM_WORKER);
   }
   else {
-    JS_GC(aCx);
+    js::GCForReason(aCx, js::gcreason::DOM_WORKER);
   }
 
   if (aCollectChildren) {
diff --git a/js/src/gc/Statistics.cpp b/js/src/gc/Statistics.cpp
index b03b7020bb4f..b1a1197ca116 100644
--- a/js/src/gc/Statistics.cpp
+++ b/js/src/gc/Statistics.cpp
@@ -38,6 +38,7 @@
  * ***** END LICENSE BLOCK ***** */
 
 #include <stdio.h>
+#include <ctype.h>
 
 #include "jscntxt.h"
 #include "jscrashformat.h"
@@ -52,6 +53,22 @@
 namespace js {
 namespace gcstats {
 
+static const char *
+ExplainReason(gcreason::Reason reason)
+{
+    switch (reason) {
+#define SWITCH_REASON(name)                     \
+        case gcreason::name:                    \
+          return #name;
+        GCREASONS(SWITCH_REASON)
+
+        default:
+          JS_NOT_REACHED("bad GC reason");
+          return "?";
+#undef SWITCH_REASON
+    }
+}
+
 Statistics::ColumnInfo::ColumnInfo(const char *title, double t, double total)
   : title(title)
 {
@@ -117,8 +134,8 @@ Statistics::makeTable(ColumnInfo *cols)
 }
 
 Statistics::Statistics(JSRuntime *rt)
-  : runtime(rt)
-  , triggerReason(PUBLIC_API) //dummy reason to satisfy makeTable
+  : runtime(rt),
+    triggerReason(gcreason::NO_REASON)
 {
     PodArrayZero(counts);
     PodArrayZero(totals);
@@ -178,7 +195,7 @@ struct GCCrashData
 };
 
 void
-Statistics::beginGC(JSCompartment *comp, Reason reason)
+Statistics::beginGC(JSCompartment *comp, gcreason::Reason reason)
 {
     compartment = comp;
 
@@ -276,7 +293,6 @@ Statistics::endGC()
     if (JSAccumulateTelemetryDataCallback cb = runtime->telemetryCallback) {
         (*cb)(JS_TELEMETRY_GC_REASON, triggerReason);
         (*cb)(JS_TELEMETRY_GC_IS_COMPARTMENTAL, compartment ? 1 : 0);
-        (*cb)(JS_TELEMETRY_GC_IS_SHAPE_REGEN, 0);
         (*cb)(JS_TELEMETRY_GC_MS, t(PHASE_GC));
         (*cb)(JS_TELEMETRY_GC_MARK_MS, t(PHASE_MARK));
         (*cb)(JS_TELEMETRY_GC_SWEEP_MS, t(PHASE_SWEEP));
diff --git a/js/src/gc/Statistics.h b/js/src/gc/Statistics.h
index 0597a94db72e..497efaca6072 100644
--- a/js/src/gc/Statistics.h
+++ b/js/src/gc/Statistics.h
@@ -42,6 +42,7 @@
 
 #include <string.h>
 
+#include "jsfriendapi.h"
 #include "jspubtd.h"
 #include "jsutil.h"
 
@@ -50,32 +51,6 @@ struct JSCompartment;
 namespace js {
 namespace gcstats {
 
-enum Reason {
-    PUBLIC_API,
-    MAYBEGC,
-    LASTCONTEXT,
-    DESTROYCONTEXT,
-    LASTDITCH,
-    TOOMUCHMALLOC,
-    ALLOCTRIGGER,
-    CHUNK,
-    SHAPE,
-    REFILL
-};
-static const int NUM_REASONS = REFILL + 1;
-
-static inline const char *
-ExplainReason(Reason r)
-{
-    static const char *strs[] = {"  API", "Maybe", "LastC", "DestC", "LastD",
-                                 "Mallc", "Alloc", "Chunk", "Shape", "Refil"};
-
-    JS_ASSERT(strcmp(strs[SHAPE], "Shape") == 0 &&
-              sizeof(strs) / sizeof(strs[0]) == NUM_REASONS);
-
-    return strs[r];
-}
-
 enum Phase {
     PHASE_GC,
     PHASE_MARK,
@@ -103,7 +78,7 @@ struct Statistics {
     Statistics(JSRuntime *rt);
     ~Statistics();
 
-    void beginGC(JSCompartment *comp, Reason reason);
+    void beginGC(JSCompartment *comp, gcreason::Reason reason);
     void endGC();
 
     void beginPhase(Phase phase);
@@ -122,7 +97,7 @@ struct Statistics {
     FILE *fp;
     bool fullFormat;
 
-    Reason triggerReason;
+    gcreason::Reason triggerReason;
     JSCompartment *compartment;
 
     uint64_t phaseStarts[PHASE_LIMIT];
@@ -140,8 +115,8 @@ struct Statistics {
 
     struct ColumnInfo {
         const char *title;
-        char str[12];
-        char totalStr[12];
+        char str[32];
+        char totalStr[32];
         int width;
 
         ColumnInfo() {}
@@ -155,7 +130,8 @@ struct Statistics {
 };
 
 struct AutoGC {
-    AutoGC(Statistics &stats, JSCompartment *comp, Reason reason JS_GUARD_OBJECT_NOTIFIER_PARAM)
+    AutoGC(Statistics &stats, JSCompartment *comp, gcreason::Reason reason
+           JS_GUARD_OBJECT_NOTIFIER_PARAM)
       : stats(stats) { JS_GUARD_OBJECT_NOTIFIER_INIT; stats.beginGC(comp, reason); }
     ~AutoGC() { stats.endGC(); }
 
diff --git a/js/src/jsapi.cpp b/js/src/jsapi.cpp
index bea809ec64b9..874cff974d37 100644
--- a/js/src/jsapi.cpp
+++ b/js/src/jsapi.cpp
@@ -735,6 +735,7 @@ JSRuntime::JSRuntime()
     gcIsNeeded(0),
     gcWeakMapList(NULL),
     gcStats(thisFromCtor()),
+    gcTriggerReason(gcreason::NO_REASON),
     gcTriggerCompartment(NULL),
     gcCurrentCompartment(NULL),
     gcCheckCompartment(NULL),
@@ -2857,7 +2858,7 @@ JS_CompartmentGC(JSContext *cx, JSCompartment *comp)
     JS_ASSERT(comp != cx->runtime->atomsCompartment);
 
     js::gc::VerifyBarriers(cx, true);
-    js_GC(cx, comp, GC_NORMAL, gcstats::PUBLIC_API);
+    js_GC(cx, comp, GC_NORMAL, gcreason::API);
 }
 
 JS_PUBLIC_API(void)
diff --git a/js/src/jscntxt.cpp b/js/src/jscntxt.cpp
index 816a426e7793..e781da8f3a3f 100644
--- a/js/src/jscntxt.cpp
+++ b/js/src/jscntxt.cpp
@@ -323,13 +323,13 @@ js_DestroyContext(JSContext *cx, JSDestroyContextMode mode)
 #endif
 
         if (last) {
-            js_GC(cx, NULL, GC_NORMAL, gcstats::LASTCONTEXT);
+            js_GC(cx, NULL, GC_NORMAL, gcreason::LAST_CONTEXT);
 
             /* Take the runtime down, now that it has no contexts or atoms. */
             JS_LOCK_GC(rt);
         } else {
             if (mode == JSDCM_FORCE_GC)
-                js_GC(cx, NULL, GC_NORMAL, gcstats::DESTROYCONTEXT);
+                js_GC(cx, NULL, GC_NORMAL, gcreason::DESTROY_CONTEXT);
             else if (mode == JSDCM_MAYBE_GC)
                 JS_MaybeGC(cx);
 
@@ -1179,7 +1179,7 @@ JSContext::runningWithTrustedPrincipals() const
 JS_FRIEND_API(void)
 JSRuntime::onTooMuchMalloc()
 {
-    TriggerGC(this, gcstats::TOOMUCHMALLOC);
+    TriggerGC(this, gcreason::TOO_MUCH_MALLOC);
 }
 
 JS_FRIEND_API(void *)
diff --git a/js/src/jscntxt.h b/js/src/jscntxt.h
index 73896ec5dd67..3bef1a46cfad 100644
--- a/js/src/jscntxt.h
+++ b/js/src/jscntxt.h
@@ -318,7 +318,7 @@ struct JSRuntime
     js::gcstats::Statistics gcStats;
 
     /* The reason that an interrupt-triggered GC should be called. */
-    js::gcstats::Reason gcTriggerReason;
+    js::gcreason::Reason gcTriggerReason;
 
     /* Pre-allocated space for the GC mark stack. */
     uintptr_t           gcMarkStackArray[js::MARK_STACK_LENGTH];
diff --git a/js/src/jsfriendapi.cpp b/js/src/jsfriendapi.cpp
index 3f92643de0ba..d05d02243adf 100644
--- a/js/src/jsfriendapi.cpp
+++ b/js/src/jsfriendapi.cpp
@@ -128,9 +128,15 @@ JS_NewObjectWithUniqueType(JSContext *cx, JSClass *clasp, JSObject *proto, JSObj
 }
 
 JS_FRIEND_API(void)
-JS_ShrinkingGC(JSContext *cx)
+js::GCForReason(JSContext *cx, gcreason::Reason reason)
 {
-    js_GC(cx, NULL, GC_SHRINK, gcstats::PUBLIC_API);
+    js_GC(cx, NULL, GC_NORMAL, reason);
+}
+
+JS_FRIEND_API(void)
+js::ShrinkingGC(JSContext *cx, gcreason::Reason reason)
+{
+    js_GC(cx, NULL, GC_SHRINK, reason);
 }
 
 JS_FRIEND_API(void)
diff --git a/js/src/jsfriendapi.h b/js/src/jsfriendapi.h
index 903e561d7cd7..f178d6f207ab 100644
--- a/js/src/jsfriendapi.h
+++ b/js/src/jsfriendapi.h
@@ -72,9 +72,6 @@ JS_NewObjectWithUniqueType(JSContext *cx, JSClass *clasp, JSObject *proto, JSObj
 extern JS_FRIEND_API(uint32_t)
 JS_ObjectCountDynamicSlots(JSObject *obj);
 
-extern JS_FRIEND_API(void)
-JS_ShrinkingGC(JSContext *cx);
-
 extern JS_FRIEND_API(void)
 JS_ShrinkGCBuffers(JSRuntime *rt);
 
@@ -101,7 +98,6 @@ JS_TraceShapeCycleCollectorChildren(JSTracer *trc, void *shape);
 enum {
     JS_TELEMETRY_GC_REASON,
     JS_TELEMETRY_GC_IS_COMPARTMENTAL,
-    JS_TELEMETRY_GC_IS_SHAPE_REGEN,
     JS_TELEMETRY_GC_MS,
     JS_TELEMETRY_GC_MARK_MS,
     JS_TELEMETRY_GC_SWEEP_MS
@@ -572,6 +568,56 @@ GetRuntimeCompartments(JSRuntime *rt);
 extern JS_FRIEND_API(size_t)
 SizeOfJSContext();
 
+#define GCREASONS(D)                            \
+    /* Reasons internal to the JS engine */     \
+    D(API)                                      \
+    D(MAYBEGC)                                  \
+    D(LAST_CONTEXT)                             \
+    D(DESTROY_CONTEXT)                          \
+    D(LAST_DITCH)                               \
+    D(TOO_MUCH_MALLOC)                          \
+    D(ALLOC_TRIGGER)                            \
+    D(UNUSED1) /* was CHUNK */                  \
+    D(UNUSED2) /* was SHAPE */                  \
+    D(UNUSED3) /* was REFILL */                 \
+                                                \
+    /* Reasons from Firefox */                  \
+    D(DOM_WINDOW_UTILS)                         \
+    D(COMPONENT_UTILS)                          \
+    D(MEM_PRESSURE)                             \
+    D(CC_WAITING)                               \
+    D(CC_FORCED)                                \
+    D(LOAD_END)                                 \
+    D(POST_COMPARTMENT)                         \
+    D(PAGE_HIDE)                                \
+    D(NSJSCONTEXT_DESTROY)                      \
+    D(SET_NEW_DOCUMENT)                         \
+    D(SET_DOC_SHELL)                            \
+    D(DOM_UTILS)                                \
+    D(DOM_IPC)                                  \
+    D(DOM_WORKER)                               \
+    D(INTER_SLICE_GC)                           \
+    D(REFRESH_FRAME)
+
+namespace gcreason {
+
+/* GCReasons will end up looking like JSGC_MAYBEGC */
+enum Reason {
+#define MAKE_REASON(name) name,
+    GCREASONS(MAKE_REASON)
+#undef MAKE_REASON
+    NO_REASON,
+    NUM_REASONS
+};
+
+} /* namespace gcreason */
+
+extern JS_FRIEND_API(void)
+GCForReason(JSContext *cx, gcreason::Reason reason);
+
+extern JS_FRIEND_API(void)
+ShrinkingGC(JSContext *cx, gcreason::Reason reason);
+
 extern JS_FRIEND_API(bool)
 IsIncrementalBarrierNeeded(JSRuntime *rt);
 
diff --git a/js/src/jsgc.cpp b/js/src/jsgc.cpp
index 176ce34ccd6c..08a1b7feeb32 100644
--- a/js/src/jsgc.cpp
+++ b/js/src/jsgc.cpp
@@ -742,7 +742,7 @@ Chunk::allocateArena(JSCompartment *comp, AllocKind thingKind)
     rt->gcBytes += ArenaSize;
     comp->gcBytes += ArenaSize;
     if (comp->gcBytes >= comp->gcTriggerBytes)
-        TriggerCompartmentGC(comp, gcstats::ALLOCTRIGGER);
+        TriggerCompartmentGC(comp, gcreason::ALLOC_TRIGGER);
 
     return aheader;
 }
@@ -1647,7 +1647,7 @@ RunLastDitchGC(JSContext *cx)
 
     /* The last ditch GC preserves all atoms. */
     AutoKeepAtoms keep(rt);
-    js_GC(cx, rt->gcTriggerCompartment, GC_NORMAL, gcstats::LASTDITCH);
+    js_GC(cx, rt->gcTriggerCompartment, GC_NORMAL, gcreason::LAST_DITCH);
 }
 
 /* static */ void *
@@ -2137,7 +2137,7 @@ MarkRuntime(JSTracer *trc)
 }
 
 void
-TriggerGC(JSRuntime *rt, gcstats::Reason reason)
+TriggerGC(JSRuntime *rt, gcreason::Reason reason)
 {
     JS_ASSERT(rt->onOwnerThread());
 
@@ -2152,7 +2152,7 @@ TriggerGC(JSRuntime *rt, gcstats::Reason reason)
 }
 
 void
-TriggerCompartmentGC(JSCompartment *comp, gcstats::Reason reason)
+TriggerCompartmentGC(JSCompartment *comp, gcreason::Reason reason)
 {
     JSRuntime *rt = comp->rt;
     JS_ASSERT(!rt->gcRunning);
@@ -2198,18 +2198,18 @@ MaybeGC(JSContext *cx)
     JS_ASSERT(rt->onOwnerThread());
 
     if (rt->gcZeal()) {
-        js_GC(cx, NULL, GC_NORMAL, gcstats::MAYBEGC);
+        js_GC(cx, NULL, GC_NORMAL, gcreason::MAYBEGC);
         return;
     }
 
     JSCompartment *comp = cx->compartment;
     if (rt->gcIsNeeded) {
-        js_GC(cx, (comp == rt->gcTriggerCompartment) ? comp : NULL, GC_NORMAL, gcstats::MAYBEGC);
+        js_GC(cx, (comp == rt->gcTriggerCompartment) ? comp : NULL, GC_NORMAL, gcreason::MAYBEGC);
         return;
     }
 
     if (comp->gcBytes > 8192 && comp->gcBytes >= 3 * (comp->gcTriggerBytes / 4)) {
-        js_GC(cx, (rt->gcMode == JSGC_MODE_COMPARTMENT) ? comp : NULL, GC_NORMAL, gcstats::MAYBEGC);
+        js_GC(cx, (rt->gcMode == JSGC_MODE_COMPARTMENT) ? comp : NULL, GC_NORMAL, gcreason::MAYBEGC);
         return;
     }
 
@@ -2223,7 +2223,7 @@ MaybeGC(JSContext *cx)
         if (rt->gcChunkAllocationSinceLastGC ||
             rt->gcNumArenasFreeCommitted > FreeCommittedArenasThreshold)
         {
-            js_GC(cx, NULL, GC_SHRINK, gcstats::MAYBEGC);
+            js_GC(cx, NULL, GC_SHRINK, gcreason::MAYBEGC);
         } else {
             rt->gcNextFullGCTime = now + GC_IDLE_FULL_SPAN;
         }
@@ -2966,7 +2966,7 @@ GCCycle(JSContext *cx, JSCompartment *comp, JSGCInvocationKind gckind)
 }
 
 void
-js_GC(JSContext *cx, JSCompartment *comp, JSGCInvocationKind gckind, gcstats::Reason reason)
+js_GC(JSContext *cx, JSCompartment *comp, JSGCInvocationKind gckind, gcreason::Reason reason)
 {
     JSRuntime *rt = cx->runtime;
     JS_AbortIfWrongThread(rt);
diff --git a/js/src/jsgc.h b/js/src/jsgc.h
index 594c1f628a6c..7863f1118ba1 100644
--- a/js/src/jsgc.h
+++ b/js/src/jsgc.h
@@ -1382,11 +1382,11 @@ MarkContext(JSTracer *trc, JSContext *acx);
 
 /* Must be called with GC lock taken. */
 extern void
-TriggerGC(JSRuntime *rt, js::gcstats::Reason reason);
+TriggerGC(JSRuntime *rt, js::gcreason::Reason reason);
 
 /* Must be called with GC lock taken. */
 extern void
-TriggerCompartmentGC(JSCompartment *comp, js::gcstats::Reason reason);
+TriggerCompartmentGC(JSCompartment *comp, js::gcreason::Reason reason);
 
 extern void
 MaybeGC(JSContext *cx);
@@ -1409,7 +1409,7 @@ typedef enum JSGCInvocationKind {
 
 /* Pass NULL for |comp| to get a full GC. */
 extern void
-js_GC(JSContext *cx, JSCompartment *comp, JSGCInvocationKind gckind, js::gcstats::Reason r);
+js_GC(JSContext *cx, JSCompartment *comp, JSGCInvocationKind gckind, js::gcreason::Reason r);
 
 namespace js {
 
diff --git a/js/xpconnect/idl/nsIXPConnect.idl b/js/xpconnect/idl/nsIXPConnect.idl
index 04a58b17316e..4de0430fc80f 100644
--- a/js/xpconnect/idl/nsIXPConnect.idl
+++ b/js/xpconnect/idl/nsIXPConnect.idl
@@ -390,9 +390,15 @@ interface nsIXPCFunctionThisTranslator : nsISupports
 #define NS_XPCONNECT_CID \
 { 0xcb6593e0, 0xf9b2, 0x11d2, \
     { 0xbd, 0xd6, 0x0, 0x0, 0x64, 0x65, 0x73, 0x74 } }
+
+enum nsGCType {
+    nsGCNormal,
+    nsGCShrinking,
+    nsGCIncremental
+};
 %}
 
-[uuid(241e6db3-e018-4d99-b976-c782a05f9c77)]
+[uuid(686bb1d0-4711-11e1-b86c-0800200c9a66)]
 interface nsIXPConnect : nsISupports
 {
 %{ C++
@@ -723,8 +729,10 @@ interface nsIXPConnect : nsISupports
 
     /**
      * Trigger a JS garbage collection.
+     * Use a js::gcreason::Reason from jsfriendapi.h for the kind.
+     * Use the nsGCType enum for the kind.
      */
-    void GarbageCollect(in boolean shrinkingGC);
+    void GarbageCollect(in PRUint32 reason, in PRUint32 kind);
 
     /**
      * Define quick stubs on the given object, @a proto.
diff --git a/js/xpconnect/src/XPCComponents.cpp b/js/xpconnect/src/XPCComponents.cpp
index 0b094d899a05..716cfdb78692 100644
--- a/js/xpconnect/src/XPCComponents.cpp
+++ b/js/xpconnect/src/XPCComponents.cpp
@@ -3600,7 +3600,7 @@ nsXPCComponents_Utils::GetWeakReference(const JS::Value &object, JSContext *cx,
 NS_IMETHODIMP
 nsXPCComponents_Utils::ForceGC(JSContext *cx)
 {
-    JS_GC(cx);
+    js::GCForReason(cx, js::gcreason::COMPONENT_UTILS);
     return NS_OK;
 }
 
@@ -3608,7 +3608,7 @@ nsXPCComponents_Utils::ForceGC(JSContext *cx)
 NS_IMETHODIMP
 nsXPCComponents_Utils::ForceShrinkingGC(JSContext *cx)
 {
-    JS_ShrinkingGC(cx);
+    js::ShrinkingGC(cx, js::gcreason::COMPONENT_UTILS);
     return NS_OK;
 }
 
@@ -3636,9 +3636,9 @@ class PreciseGCRunnable : public nsRunnable
         }
 
         if (mShrinking)
-            JS_ShrinkingGC(mCx);
+            js::ShrinkingGC(mCx, js::gcreason::COMPONENT_UTILS);
         else
-            JS_GC(mCx);
+            js::GCForReason(mCx, js::gcreason::COMPONENT_UTILS);
 
         mCallback->Callback();
         return NS_OK;
diff --git a/js/xpconnect/src/XPCJSRuntime.cpp b/js/xpconnect/src/XPCJSRuntime.cpp
index 692462de1f5b..63b84fde9f32 100644
--- a/js/xpconnect/src/XPCJSRuntime.cpp
+++ b/js/xpconnect/src/XPCJSRuntime.cpp
@@ -1870,9 +1870,6 @@ AccumulateTelemetryCallback(int id, uint32_t sample)
       case JS_TELEMETRY_GC_IS_COMPARTMENTAL:
         Telemetry::Accumulate(Telemetry::GC_IS_COMPARTMENTAL, sample);
         break;
-      case JS_TELEMETRY_GC_IS_SHAPE_REGEN:
-        Telemetry::Accumulate(Telemetry::GC_IS_SHAPE_REGEN, sample);
-        break;
       case JS_TELEMETRY_GC_MS:
         Telemetry::Accumulate(Telemetry::GC_MS, sample);
         break;
diff --git a/js/xpconnect/src/nsXPConnect.cpp b/js/xpconnect/src/nsXPConnect.cpp
index d02af55cebc1..5c8f27e3a49f 100644
--- a/js/xpconnect/src/nsXPConnect.cpp
+++ b/js/xpconnect/src/nsXPConnect.cpp
@@ -365,7 +365,7 @@ nsXPConnect::NeedCollect()
 }
 
 void
-nsXPConnect::Collect(bool shrinkingGC)
+nsXPConnect::Collect(PRUint32 reason, PRUint32 kind)
 {
     // We're dividing JS objects into 2 categories:
     //
@@ -424,16 +424,20 @@ nsXPConnect::Collect(bool shrinkingGC)
     // XPCCallContext::Init we disable the conservative scanner if that call
     // has started the request on this thread.
     js::AutoSkipConservativeScan ascs(cx);
-    if (shrinkingGC)
-        JS_ShrinkingGC(cx);
-    else
-        JS_GC(cx);
+    MOZ_ASSERT(reason < js::gcreason::NUM_REASONS);
+    js::gcreason::Reason gcreason = (js::gcreason::Reason)reason;
+    if (kind == nsGCShrinking) {
+        js::ShrinkingGC(cx, gcreason);
+    } else {
+        MOZ_ASSERT(kind == nsGCNormal);
+        js::GCForReason(cx, gcreason);
+    }
 }
 
 NS_IMETHODIMP
-nsXPConnect::GarbageCollect(bool shrinkingGC)
+nsXPConnect::GarbageCollect(PRUint32 reason, PRUint32 kind)
 {
-    Collect(shrinkingGC);
+    Collect(reason, kind);
     return NS_OK;
 }
 
diff --git a/js/xpconnect/src/xpcprivate.h b/js/xpconnect/src/xpcprivate.h
index f54f54c24012..d4cc30b708b0 100644
--- a/js/xpconnect/src/xpcprivate.h
+++ b/js/xpconnect/src/xpcprivate.h
@@ -549,7 +549,7 @@ public:
     virtual nsresult FinishCycleCollection();
     virtual nsCycleCollectionParticipant *ToParticipant(void *p);
     virtual bool NeedCollect();
-    virtual void Collect(bool shrinkingGC=false);
+    virtual void Collect(PRUint32 reason, PRUint32 kind);
 #ifdef DEBUG_CC
     virtual void PrintAllReferencesTo(void *p);
 #endif
diff --git a/layout/base/nsDocumentViewer.cpp b/layout/base/nsDocumentViewer.cpp
index 486e5415ff19..bc0eb1673742 100644
--- a/layout/base/nsDocumentViewer.cpp
+++ b/layout/base/nsDocumentViewer.cpp
@@ -198,6 +198,8 @@ static const char sPrintOptionsContractID[]         = "@mozilla.org/gfx/printset
 
 #include "mozilla/dom/Element.h"
 
+#include "jsfriendapi.h"
+
 using namespace mozilla;
 
 #ifdef NS_DEBUG
@@ -1287,7 +1289,7 @@ DocumentViewerImpl::PageHide(bool aIsUnload)
 
   if (aIsUnload) {
     // Poke the GC. The window might be collectable garbage now.
-    nsJSContext::PokeGC();
+    nsJSContext::PokeGC(js::gcreason::PAGE_HIDE);
 
     // if Destroy() was called during OnPageHide(), mDocument is nsnull.
     NS_ENSURE_STATE(mDocument);
diff --git a/toolkit/components/telemetry/TelemetryHistograms.h b/toolkit/components/telemetry/TelemetryHistograms.h
index 4b3feb5a8f71..3e7f7701c481 100644
--- a/toolkit/components/telemetry/TelemetryHistograms.h
+++ b/toolkit/components/telemetry/TelemetryHistograms.h
@@ -75,7 +75,6 @@ HISTOGRAM(CYCLE_COLLECTOR_TIME_BETWEEN, 1, 120, 50, EXPONENTIAL, "Time spent in
  */
 HISTOGRAM(GC_REASON, 1, 20, 20, LINEAR, "Reason (enum value) for initiating a GC")
 HISTOGRAM_BOOLEAN(GC_IS_COMPARTMENTAL, "Is it a compartmental GC?")
-HISTOGRAM_BOOLEAN(GC_IS_SHAPE_REGEN, "Is it a shape regenerating GC?")
 HISTOGRAM(GC_MS, 1, 10000, 50, EXPONENTIAL, "Time spent running JS GC (ms)")
 HISTOGRAM(GC_MARK_MS, 1, 10000, 50, EXPONENTIAL, "Time spent running JS GC mark phase (ms)")
 HISTOGRAM(GC_SWEEP_MS, 1, 10000, 50, EXPONENTIAL, "Time spent running JS GC sweep phase (ms)")
diff --git a/xpcom/base/nsCycleCollector.cpp b/xpcom/base/nsCycleCollector.cpp
index 6fd9b9b3ed78..d9aad7aa86c6 100644
--- a/xpcom/base/nsCycleCollector.cpp
+++ b/xpcom/base/nsCycleCollector.cpp
@@ -2823,7 +2823,7 @@ nsCycleCollector::GCIfNeeded(bool aForceGC)
     // rt->Collect() must be called from the main thread,
     // because it invokes XPCJSRuntime::GCCallback(cx, JSGC_BEGIN)
     // which returns false if not in the main thread.
-    rt->Collect();
+    rt->Collect(js::gcreason::CC_FORCED, nsGCNormal);
 #ifdef COLLECT_TIME_DEBUG
     printf("cc: GC() took %lldms\n", (PR_Now() - start) / PR_USEC_PER_MSEC);
 #endif
diff --git a/xpcom/base/nsCycleCollector.h b/xpcom/base/nsCycleCollector.h
index 7dabe60e5dab..61a258355c2d 100644
--- a/xpcom/base/nsCycleCollector.h
+++ b/xpcom/base/nsCycleCollector.h
@@ -106,9 +106,10 @@ struct nsCycleCollectionJSRuntime : public nsCycleCollectionLanguageRuntime
     virtual bool NeedCollect() = 0;
 
     /**
-     * Runs the JavaScript GC.
+     * Runs the JavaScript GC. |reason| is a gcreason::Reason from jsfriendapi.h.
+     * |kind| is a nsGCType from nsIXPConnect.idl.
      */
-    virtual void Collect(bool shrinkingGC = false) = 0;
+    virtual void Collect(PRUint32 reason, PRUint32 kind) = 0;
 };
 
 #ifdef DEBUG