Backed out changeset 5e01d4124eae (bug 833143) on suspicion of triggering assertion CompositorThreadHolder::IsInCompositorThread() on Windows 8 x64 M-e10s. r=backout

toolkit/xre/nsXREDirProvider.cpp

@@ -1239,6 +1239,15 @@ nsXREDirProvider::DoShutdown()
       static const char16_t kShutdownPersist[] = u"shutdown-persist";
       obsSvc->NotifyObservers(nullptr, "profile-change-net-teardown", kShutdownPersist);
       obsSvc->NotifyObservers(nullptr, "profile-change-teardown", kShutdownPersist);
+
+      // Phase 2c: Now that things are torn down, force JS GC so that things which depend on
+      // resources which are about to go away in "profile-before-change" are destroyed first.
+
+      if (JSContext* cx = dom::danger::GetJSContext()) {
+        JS_GC(cx);
+      }
+
+      // Phase 3: Notify observers of a profile change
       obsSvc->NotifyObservers(nullptr, "profile-before-change", kShutdownPersist);
       obsSvc->NotifyObservers(nullptr, "profile-before-change-qm", kShutdownPersist);
       obsSvc->NotifyObservers(nullptr, "profile-before-change-telemetry", kShutdownPersist);