--- a/toolkit/components/url-classifier/nsUrlClassifierProxies.cpp
+++ b/toolkit/components/url-classifier/nsUrlClassifierProxies.cpp
@@ -233,22 +233,28 @@ UrlClassifierUpdateObserverProxy::Update
 {
   mTarget->UpdateUrlRequested(mURL, mTable, mServerMAC);
   return NS_OK;
 }
 
 NS_IMETHODIMP
 UrlClassifierUpdateObserverProxy::RekeyRequested()
 {
-  nsCOMPtr<nsIRunnable> r =
-    NS_NewRunnableMethod(mTarget, &nsIUrlClassifierUpdateObserver::RekeyRequested);
+  nsCOMPtr<nsIRunnable> r = new RekeyRequestedRunnable(mTarget);
   return NS_DispatchToMainThread(r);
 }
 
 NS_IMETHODIMP
+UrlClassifierUpdateObserverProxy::RekeyRequestedRunnable::Run()
+{
+  mTarget->RekeyRequested();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
 UrlClassifierUpdateObserverProxy::StreamFinished(nsresult aStatus,
                                                  uint32_t aDelay)
 {
   nsCOMPtr<nsIRunnable> r =
     new StreamFinishedRunnable(mTarget, aStatus, aDelay);
   return NS_DispatchToMainThread(r);
 }
 

--- a/toolkit/components/url-classifier/nsUrlClassifierProxies.h
+++ b/toolkit/components/url-classifier/nsUrlClassifierProxies.h
@@ -2,16 +2,17 @@
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #ifndef nsUrlClassifierProxies_h
 #define nsUrlClassifierProxies_h
 
 #include "nsIUrlClassifierDBService.h"
+#include "nsProxyRelease.h"
 #include "nsThreadUtils.h"
 #include "mozilla/Attributes.h"
 #include "nsIPrincipal.h"
 #include "LookupCache.h"
 
 using namespace mozilla::safebrowsing;
 
 /**
@@ -157,150 +158,163 @@ private:
 
 // The remaining classes here are all proxies to the main thread
 
 class UrlClassifierLookupCallbackProxy MOZ_FINAL :
   public nsIUrlClassifierLookupCallback
 {
 public:
   UrlClassifierLookupCallbackProxy(nsIUrlClassifierLookupCallback* aTarget)
-    : mTarget(aTarget)
+    : mTarget(new nsMainThreadPtrHolder<nsIUrlClassifierLookupCallback>(aTarget))
   { }
 
   NS_DECL_ISUPPORTS
   NS_DECL_NSIURLCLASSIFIERLOOKUPCALLBACK
 
   class LookupCompleteRunnable : public nsRunnable
   {
   public:
-    LookupCompleteRunnable(nsIUrlClassifierLookupCallback* aTarget,
+    LookupCompleteRunnable(nsMainThreadPtrHolder<nsIUrlClassifierLookupCallback>* aTarget,
                            LookupResultArray *aResults)
       : mTarget(aTarget)
       , mResults(aResults)
     { }
 
     NS_DECL_NSIRUNNABLE
 
   private:
-    nsCOMPtr<nsIUrlClassifierLookupCallback> mTarget;
+    nsMainThreadPtrHandle<nsIUrlClassifierLookupCallback> mTarget;
     LookupResultArray * mResults;
   };
 
 private:
-  nsCOMPtr<nsIUrlClassifierLookupCallback> mTarget;
+  nsMainThreadPtrHandle<nsIUrlClassifierLookupCallback> mTarget;
 };
 
 class UrlClassifierCallbackProxy MOZ_FINAL : public nsIUrlClassifierCallback
 {
 public:
   UrlClassifierCallbackProxy(nsIUrlClassifierCallback* aTarget)
-    : mTarget(aTarget)
+    : mTarget(new nsMainThreadPtrHolder<nsIUrlClassifierCallback>(aTarget))
   { }
 
   NS_DECL_ISUPPORTS
   NS_DECL_NSIURLCLASSIFIERCALLBACK
 
   class HandleEventRunnable : public nsRunnable
   {
   public:
-    HandleEventRunnable(nsIUrlClassifierCallback* aTarget,
+    HandleEventRunnable(nsMainThreadPtrHolder<nsIUrlClassifierCallback>* aTarget,
                         const nsACString& aValue)
       : mTarget(aTarget)
       , mValue(aValue)
     { }
 
     NS_DECL_NSIRUNNABLE
 
   private:
-    nsCOMPtr<nsIUrlClassifierCallback> mTarget;
+    nsMainThreadPtrHandle<nsIUrlClassifierCallback> mTarget;
     nsCString mValue;
   };
 
 private:
-  nsCOMPtr<nsIUrlClassifierCallback> mTarget;
+  nsMainThreadPtrHandle<nsIUrlClassifierCallback> mTarget;
 };
 
 class UrlClassifierUpdateObserverProxy MOZ_FINAL :
   public nsIUrlClassifierUpdateObserver
 {
 public:
   UrlClassifierUpdateObserverProxy(nsIUrlClassifierUpdateObserver* aTarget)
-    : mTarget(aTarget)
+    : mTarget(new nsMainThreadPtrHolder<nsIUrlClassifierUpdateObserver>(aTarget))
   { }
 
   NS_DECL_ISUPPORTS
   NS_DECL_NSIURLCLASSIFIERUPDATEOBSERVER
 
   class UpdateUrlRequestedRunnable : public nsRunnable
   {
   public:
-    UpdateUrlRequestedRunnable(nsIUrlClassifierUpdateObserver* aTarget,
+    UpdateUrlRequestedRunnable(nsMainThreadPtrHolder<nsIUrlClassifierUpdateObserver>* aTarget,
                                const nsACString& aURL,
                                const nsACString& aTable,
                                const nsACString& aServerMAC)
       : mTarget(aTarget)
       , mURL(aURL)
       , mTable(aTable)
       , mServerMAC(aServerMAC)
     { }
 
     NS_DECL_NSIRUNNABLE
 
   private:
-    nsCOMPtr<nsIUrlClassifierUpdateObserver> mTarget;
+    nsMainThreadPtrHandle<nsIUrlClassifierUpdateObserver> mTarget;
     nsCString mURL, mTable, mServerMAC;
   };
 
+  class RekeyRequestedRunnable : public nsRunnable
+  {
+  public:
+    RekeyRequestedRunnable(nsMainThreadPtrHolder<nsIUrlClassifierUpdateObserver>* aTarget)
+      : mTarget(aTarget)
+    { }
+
+    NS_DECL_NSIRUNNABLE
+
+  private:
+    nsMainThreadPtrHandle<nsIUrlClassifierUpdateObserver> mTarget;
+  };
+
   class StreamFinishedRunnable : public nsRunnable
   {
   public:
-    StreamFinishedRunnable(nsIUrlClassifierUpdateObserver* aTarget,
+    StreamFinishedRunnable(nsMainThreadPtrHolder<nsIUrlClassifierUpdateObserver>* aTarget,
                            nsresult aStatus, uint32_t aDelay)
       : mTarget(aTarget)
       , mStatus(aStatus)
       , mDelay(aDelay)
     { }
 
     NS_DECL_NSIRUNNABLE
 
   private:
-    nsCOMPtr<nsIUrlClassifierUpdateObserver> mTarget;
+    nsMainThreadPtrHandle<nsIUrlClassifierUpdateObserver> mTarget;
     nsresult mStatus;
     uint32_t mDelay;
   };
 
   class UpdateErrorRunnable : public nsRunnable
   {
   public:
-    UpdateErrorRunnable(nsIUrlClassifierUpdateObserver* aTarget,
+    UpdateErrorRunnable(nsMainThreadPtrHolder<nsIUrlClassifierUpdateObserver>* aTarget,
                         nsresult aError)
       : mTarget(aTarget)
       , mError(aError)
     { }
 
     NS_DECL_NSIRUNNABLE
 
   private:
-    nsCOMPtr<nsIUrlClassifierUpdateObserver> mTarget;
+    nsMainThreadPtrHandle<nsIUrlClassifierUpdateObserver> mTarget;
     nsresult mError;
   };
 
   class UpdateSuccessRunnable : public nsRunnable
   {
   public:
-    UpdateSuccessRunnable(nsIUrlClassifierUpdateObserver* aTarget,
+    UpdateSuccessRunnable(nsMainThreadPtrHolder<nsIUrlClassifierUpdateObserver>* aTarget,
                           uint32_t aRequestedTimeout)
       : mTarget(aTarget)
       , mRequestedTimeout(aRequestedTimeout)
     { }
 
     NS_DECL_NSIRUNNABLE
 
   private:
-    nsCOMPtr<nsIUrlClassifierUpdateObserver> mTarget;
+    nsMainThreadPtrHandle<nsIUrlClassifierUpdateObserver> mTarget;
     uint32_t mRequestedTimeout;
   };
 
 private:
-  nsCOMPtr<nsIUrlClassifierUpdateObserver> mTarget;
+  nsMainThreadPtrHandle<nsIUrlClassifierUpdateObserver> mTarget;
 };
 
 #endif // nsUrlClassifierProxies_h