diff --git a/dom/base/nsJSEnvironment.cpp b/dom/base/nsJSEnvironment.cpp
index 7d913fce8004..5f0c683aa581 100644
--- a/dom/base/nsJSEnvironment.cpp
+++ b/dom/base/nsJSEnvironment.cpp
@@ -1294,11 +1294,10 @@ nsJSContext::GarbageCollectNow(JS::gcreason::Reason aReason,
 
   if (aIncremental == IncrementalGC) {
     MOZ_ASSERT(aShrinking == NonShrinkingGC);
-    JS::StartIncrementalGC(sRuntime, aReason, aSliceMillis);
-  } else if (aShrinking == ShrinkingGC) {
-    JS::ShrinkingGC(sRuntime, aReason);
+    JS::StartIncrementalGC(sRuntime, GC_NORMAL, aReason, aSliceMillis);
   } else {
-    JS::GCForReason(sRuntime, aReason);
+    JSGCInvocationKind gckind = aShrinking == ShrinkingGC ? GC_SHRINK : GC_NORMAL;
+    JS::GCForReason(sRuntime, gckind, aReason);
   }
 }
 
diff --git a/dom/workers/WorkerPrivate.cpp b/dom/workers/WorkerPrivate.cpp
index 47cf553b4c7c..2da1743c253c 100644
--- a/dom/workers/WorkerPrivate.cpp
+++ b/dom/workers/WorkerPrivate.cpp
@@ -6020,14 +6020,14 @@ WorkerPrivate::GarbageCollectInternal(JSContext* aCx, bool aShrinking,
     JS::PrepareForFullGC(rt);
 
     if (aShrinking) {
-      JS::ShrinkingGC(rt, JS::gcreason::DOM_WORKER);
+      JS::GCForReason(rt, GC_SHRINK, JS::gcreason::DOM_WORKER);
 
       if (!aCollectChildren) {
         LOG(("Worker %p collected idle garbage\n", this));
       }
     }
     else {
-      JS::GCForReason(rt, JS::gcreason::DOM_WORKER);
+      JS::GCForReason(rt, GC_NORMAL, JS::gcreason::DOM_WORKER);
       LOG(("Worker %p collected garbage\n", this));
     }
   }
diff --git a/js/public/GCAPI.h b/js/public/GCAPI.h
index 439fb5805163..c2da39a2356e 100644
--- a/js/public/GCAPI.h
+++ b/js/public/GCAPI.h
@@ -31,6 +31,17 @@ typedef enum JSGCMode {
     JSGC_MODE_INCREMENTAL = 2
 } JSGCMode;
 
+/*
+ * Kinds of js_GC invocation.
+ */
+typedef enum JSGCInvocationKind {
+    /* Normal invocation. */
+    GC_NORMAL = 0,
+
+    /* Minimize GC triggers and release empty GC chunks right away. */
+    GC_SHRINK = 1
+} JSGCInvocationKind;
+
 namespace JS {
 
 #define GCREASONS(D)                            \
@@ -168,20 +179,16 @@ SkipZoneForGC(Zone *zone);
  */
 
 /*
- * Performs a non-incremental collection of all selected zones. Some objects
- * that are unreachable from the program may still be alive afterwards because
- * of internal references.
+ * Performs a non-incremental collection of all selected zones.
+ *
+ * If the gckind argument is GC_NORMAL, then some objects that are unreachable
+ * from the program may still be alive afterwards because of internal
+ * references; if GC_SHRINK is passed then caches and other temporary references
+ * to objects will be cleared and all unreferenced objects will be removed from
+ * the system.
  */
 extern JS_FRIEND_API(void)
-GCForReason(JSRuntime *rt, gcreason::Reason reason);
-
-/*
- * Perform a non-incremental collection after clearing caches and other
- * temporary references to objects. This will remove all unreferenced objects
- * in the system.
- */
-extern JS_FRIEND_API(void)
-ShrinkingGC(JSRuntime *rt, gcreason::Reason reason);
+GCForReason(JSRuntime *rt, JSGCInvocationKind gckind, gcreason::Reason reason);
 
 /*
  * Incremental GC:
@@ -216,7 +223,8 @@ ShrinkingGC(JSRuntime *rt, gcreason::Reason reason);
  *       shorter than the requested interval.
  */
 extern JS_FRIEND_API(void)
-StartIncrementalGC(JSRuntime *rt, gcreason::Reason reason, int64_t millis = 0);
+StartIncrementalGC(JSRuntime *rt, JSGCInvocationKind gckind, gcreason::Reason reason,
+                   int64_t millis = 0);
 
 /*
  * Perform a slice of an ongoing incremental collection. When this function
diff --git a/js/src/builtin/TestingFunctions.cpp b/js/src/builtin/TestingFunctions.cpp
index faf5484aa35f..8718f4c8fe42 100644
--- a/js/src/builtin/TestingFunctions.cpp
+++ b/js/src/builtin/TestingFunctions.cpp
@@ -238,10 +238,8 @@ GC(JSContext *cx, unsigned argc, jsval *vp)
     else
         JS::PrepareForFullGC(cx->runtime());
 
-    if (shrinking)
-        JS::ShrinkingGC(cx->runtime(), JS::gcreason::API);
-    else
-        JS::GCForReason(cx->runtime(), JS::gcreason::API);
+    JSGCInvocationKind gckind = shrinking ? GC_SHRINK : GC_NORMAL;
+    JS::GCForReason(cx->runtime(), gckind, JS::gcreason::API);
 
     char buf[256] = { '\0' };
 #ifndef JS_MORE_DETERMINISTIC
diff --git a/js/src/jsapi-tests/testGCFinalizeCallback.cpp b/js/src/jsapi-tests/testGCFinalizeCallback.cpp
index 99673d6dd1c7..b7c681b9aabb 100644
--- a/js/src/jsapi-tests/testGCFinalizeCallback.cpp
+++ b/js/src/jsapi-tests/testGCFinalizeCallback.cpp
@@ -24,7 +24,7 @@ BEGIN_TEST(testGCFinalizeCallback)
     /* Full GC, incremental. */
     FinalizeCalls = 0;
     JS::PrepareForFullGC(rt);
-    JS::StartIncrementalGC(rt, JS::gcreason::API, 1000000);
+    JS::StartIncrementalGC(rt, GC_NORMAL, JS::gcreason::API, 1000000);
     CHECK(!rt->gc.isIncrementalGCInProgress());
     CHECK(rt->gc.isFullGc());
     CHECK(checkMultipleGroups());
@@ -41,7 +41,7 @@ BEGIN_TEST(testGCFinalizeCallback)
     /* Compartment GC, non-incremental, single compartment. */
     FinalizeCalls = 0;
     JS::PrepareZoneForGC(global1->zone());
-    JS::GCForReason(rt, JS::gcreason::API);
+    JS::GCForReason(rt, GC_NORMAL, JS::gcreason::API);
     CHECK(!rt->gc.isFullGc());
     CHECK(checkSingleGroup());
     CHECK(checkFinalizeStatus());
@@ -52,7 +52,7 @@ BEGIN_TEST(testGCFinalizeCallback)
     JS::PrepareZoneForGC(global1->zone());
     JS::PrepareZoneForGC(global2->zone());
     JS::PrepareZoneForGC(global3->zone());
-    JS::GCForReason(rt, JS::gcreason::API);
+    JS::GCForReason(rt, GC_NORMAL, JS::gcreason::API);
     CHECK(!rt->gc.isFullGc());
     CHECK(checkSingleGroup());
     CHECK(checkFinalizeStatus());
@@ -61,7 +61,7 @@ BEGIN_TEST(testGCFinalizeCallback)
     /* Compartment GC, incremental, single compartment. */
     FinalizeCalls = 0;
     JS::PrepareZoneForGC(global1->zone());
-    JS::StartIncrementalGC(rt, JS::gcreason::API, 1000000);
+    JS::StartIncrementalGC(rt, GC_NORMAL, JS::gcreason::API, 1000000);
     CHECK(!rt->gc.isIncrementalGCInProgress());
     CHECK(!rt->gc.isFullGc());
     CHECK(checkSingleGroup());
@@ -73,7 +73,7 @@ BEGIN_TEST(testGCFinalizeCallback)
     JS::PrepareZoneForGC(global1->zone());
     JS::PrepareZoneForGC(global2->zone());
     JS::PrepareZoneForGC(global3->zone());
-    JS::StartIncrementalGC(rt, JS::gcreason::API, 1000000);
+    JS::StartIncrementalGC(rt, GC_NORMAL, JS::gcreason::API, 1000000);
     CHECK(!rt->gc.isIncrementalGCInProgress());
     CHECK(!rt->gc.isFullGc());
     CHECK(checkMultipleGroups());
diff --git a/js/src/jsapi-tests/testPreserveJitCode.cpp b/js/src/jsapi-tests/testPreserveJitCode.cpp
index fd7d328a3e0c..40ee89a8d030 100644
--- a/js/src/jsapi-tests/testPreserveJitCode.cpp
+++ b/js/src/jsapi-tests/testPreserveJitCode.cpp
@@ -65,10 +65,10 @@ testPreserveJitCode(bool preserveJitCode, unsigned remainingIonScripts)
     CHECK_EQUAL(value.toInt32(), 45);
     CHECK_EQUAL(countIonScripts(global), 1u);
 
-    GCForReason(rt, gcreason::API);
+    GCForReason(rt, GC_NORMAL, gcreason::API);
     CHECK_EQUAL(countIonScripts(global), remainingIonScripts);
 
-    ShrinkingGC(rt, gcreason::API);
+    GCForReason(rt, GC_SHRINK, gcreason::API);
     CHECK_EQUAL(countIonScripts(global), 0u);
 
     return true;
diff --git a/js/src/jsapi-tests/tests.h b/js/src/jsapi-tests/tests.h
index d01113d93802..20bd5ea2f798 100644
--- a/js/src/jsapi-tests/tests.h
+++ b/js/src/jsapi-tests/tests.h
@@ -428,7 +428,7 @@ class AutoLeaveZeal
         JS_GetGCZeal(cx_, &zeal_, &frequency_);
         JS_SetGCZeal(cx_, 0, 0);
         JS::PrepareForFullGC(JS_GetRuntime(cx_));
-        JS::ShrinkingGC(JS_GetRuntime(cx_), JS::gcreason::DEBUG_GC);
+        JS::GCForReason(JS_GetRuntime(cx_), GC_SHRINK, JS::gcreason::DEBUG_GC);
     }
     ~AutoLeaveZeal() {
         JS_SetGCZeal(cx_, zeal_, frequency_);
diff --git a/js/src/jsfriendapi.cpp b/js/src/jsfriendapi.cpp
index 41aca0d0ec4f..5e88e90be572 100644
--- a/js/src/jsfriendapi.cpp
+++ b/js/src/jsfriendapi.cpp
@@ -196,21 +196,17 @@ JS::SkipZoneForGC(Zone *zone)
 }
 
 JS_FRIEND_API(void)
-JS::GCForReason(JSRuntime *rt, gcreason::Reason reason)
+JS::GCForReason(JSRuntime *rt, JSGCInvocationKind gckind, gcreason::Reason reason)
 {
-    rt->gc.gc(GC_NORMAL, reason);
+    MOZ_ASSERT(gckind == GC_NORMAL || gckind == GC_SHRINK);
+    rt->gc.gc(gckind, reason);
 }
 
 JS_FRIEND_API(void)
-JS::ShrinkingGC(JSRuntime *rt, gcreason::Reason reason)
+JS::StartIncrementalGC(JSRuntime *rt, JSGCInvocationKind gckind, gcreason::Reason reason, int64_t millis)
 {
-    rt->gc.gc(GC_SHRINK, reason);
-}
-
-JS_FRIEND_API(void)
-JS::StartIncrementalGC(JSRuntime *rt, gcreason::Reason reason, int64_t millis)
-{
-    rt->gc.startGC(GC_NORMAL, reason, millis);
+    MOZ_ASSERT(gckind == GC_NORMAL || gckind == GC_SHRINK);
+    rt->gc.startGC(gckind, reason, millis);
 }
 
 JS_FRIEND_API(void)
diff --git a/js/src/jsgc.h b/js/src/jsgc.h
index d37156aa400e..1d6002154c01 100644
--- a/js/src/jsgc.h
+++ b/js/src/jsgc.h
@@ -903,17 +903,6 @@ TraceRuntime(JSTracer *trc);
 extern void
 ReleaseAllJITCode(FreeOp *op);
 
-/*
- * Kinds of js_GC invocation.
- */
-typedef enum JSGCInvocationKind {
-    /* Normal invocation. */
-    GC_NORMAL           = 0,
-
-    /* Minimize GC triggers and release empty GC chunks right away. */
-    GC_SHRINK             = 1
-} JSGCInvocationKind;
-
 extern void
 PrepareForDebugGC(JSRuntime *rt);
 
diff --git a/js/xpconnect/src/XPCComponents.cpp b/js/xpconnect/src/XPCComponents.cpp
index e6aa4593281e..6af61cbdd8ed 100644
--- a/js/xpconnect/src/XPCComponents.cpp
+++ b/js/xpconnect/src/XPCComponents.cpp
@@ -2750,7 +2750,7 @@ nsXPCComponents_Utils::ForceGC()
 {
     JSRuntime* rt = nsXPConnect::GetRuntimeInstance()->Runtime();
     PrepareForFullGC(rt);
-    GCForReason(rt, gcreason::COMPONENT_UTILS);
+    GCForReason(rt, GC_NORMAL, gcreason::COMPONENT_UTILS);
     return NS_OK;
 }
 
@@ -2800,7 +2800,7 @@ nsXPCComponents_Utils::ForceShrinkingGC()
 {
     JSRuntime* rt = nsXPConnect::GetRuntimeInstance()->Runtime();
     PrepareForFullGC(rt);
-    ShrinkingGC(rt, gcreason::COMPONENT_UTILS);
+    GCForReason(rt, GC_SHRINK, gcreason::COMPONENT_UTILS);
     return NS_OK;
 }
 
@@ -2823,10 +2823,8 @@ class PreciseGCRunnable : public nsRunnable
         }
 
         PrepareForFullGC(rt);
-        if (mShrinking)
-            ShrinkingGC(rt, gcreason::COMPONENT_UTILS);
-        else
-            GCForReason(rt, gcreason::COMPONENT_UTILS);
+        JSGCInvocationKind gckind = mShrinking ? GC_SHRINK : GC_NORMAL;
+        GCForReason(rt, gckind, gcreason::COMPONENT_UTILS);
 
         mCallback->Callback();
         return NS_OK;
diff --git a/xpcom/base/CycleCollectedJSRuntime.cpp b/xpcom/base/CycleCollectedJSRuntime.cpp
index e4e6b5be3d4e..0e10a427c394 100644
--- a/xpcom/base/CycleCollectedJSRuntime.cpp
+++ b/xpcom/base/CycleCollectedJSRuntime.cpp
@@ -1025,7 +1025,7 @@ CycleCollectedJSRuntime::GarbageCollect(uint32_t aReason) const
   JS::gcreason::Reason gcreason = static_cast<JS::gcreason::Reason>(aReason);
 
   JS::PrepareForFullGC(mJSRuntime);
-  JS::GCForReason(mJSRuntime, gcreason);
+  JS::GCForReason(mJSRuntime, GC_NORMAL, gcreason);
 }
 
 void