--- a/netwerk/base/nsIURIMutator.idl
+++ b/netwerk/base/nsIURIMutator.idl
@@ -310,94 +310,134 @@ class MOZ_STACK_CLASS NS_MutateURI
 public:
   explicit NS_MutateURI(nsIURI* aURI);
   explicit NS_MutateURI(const char * aContractID);
 
   explicit NS_MutateURI(nsIURIMutator* m)
   {
     mStatus = m ? NS_OK : NS_ERROR_NULL_POINTER;
     mMutator = m;
+    NS_ENSURE_SUCCESS_VOID(mStatus);
   }
 
   NS_MutateURI& SetSpec(const nsACString& aSpec)
   {
+    if (NS_FAILED(mStatus)) {
+      return *this;
+    }
+    mStatus = mMutator->SetSpec(aSpec, nullptr);
     NS_ENSURE_SUCCESS(mStatus, *this);
-    mStatus = mMutator->SetSpec(aSpec, nullptr);
     return *this;
   }
   NS_MutateURI& SetScheme(const nsACString& aScheme)
   {
+    if (NS_FAILED(mStatus)) {
+      return *this;
+    }
+    mStatus = mMutator->SetScheme(aScheme, nullptr);
     NS_ENSURE_SUCCESS(mStatus, *this);
-    mStatus = mMutator->SetScheme(aScheme, nullptr);
     return *this;
   }
   NS_MutateURI& SetUserPass(const nsACString& aUserPass)
   {
+    if (NS_FAILED(mStatus)) {
+      return *this;
+    }
+    mStatus = mMutator->SetUserPass(aUserPass, nullptr);
     NS_ENSURE_SUCCESS(mStatus, *this);
-    mStatus = mMutator->SetUserPass(aUserPass, nullptr);
     return *this;
   }
   NS_MutateURI& SetUsername(const nsACString& aUsername)
   {
+    if (NS_FAILED(mStatus)) {
+      return *this;
+    }
+    mStatus = mMutator->SetUsername(aUsername, nullptr);
     NS_ENSURE_SUCCESS(mStatus, *this);
-    mStatus = mMutator->SetUsername(aUsername, nullptr);
     return *this;
   }
   NS_MutateURI& SetPassword(const nsACString& aPassword)
   {
+    if (NS_FAILED(mStatus)) {
+      return *this;
+    }
+    mStatus = mMutator->SetPassword(aPassword, nullptr);
     NS_ENSURE_SUCCESS(mStatus, *this);
-    mStatus = mMutator->SetPassword(aPassword, nullptr);
     return *this;
   }
   NS_MutateURI& SetHostPort(const nsACString& aHostPort)
   {
+    if (NS_FAILED(mStatus)) {
+      return *this;
+    }
+    mStatus = mMutator->SetHostPort(aHostPort, nullptr);
     NS_ENSURE_SUCCESS(mStatus, *this);
-    mStatus = mMutator->SetHostPort(aHostPort, nullptr);
     return *this;
   }
   NS_MutateURI& SetHost(const nsACString& aHost)
   {
+    if (NS_FAILED(mStatus)) {
+      return *this;
+    }
+    mStatus = mMutator->SetHost(aHost, nullptr);
     NS_ENSURE_SUCCESS(mStatus, *this);
-    mStatus = mMutator->SetHost(aHost, nullptr);
     return *this;
   }
   NS_MutateURI& SetPort(int32_t aPort)
   {
+    if (NS_FAILED(mStatus)) {
+      return *this;
+    }
+    mStatus = mMutator->SetPort(aPort, nullptr);
     NS_ENSURE_SUCCESS(mStatus, *this);
-    mStatus = mMutator->SetPort(aPort, nullptr);
     return *this;
   }
   NS_MutateURI& SetPathQueryRef(const nsACString& aPathQueryRef)
   {
+    if (NS_FAILED(mStatus)) {
+      return *this;
+    }
+    mStatus = mMutator->SetPathQueryRef(aPathQueryRef, nullptr);
     NS_ENSURE_SUCCESS(mStatus, *this);
-    mStatus = mMutator->SetPathQueryRef(aPathQueryRef, nullptr);
     return *this;
   }
   NS_MutateURI& SetRef(const nsACString& aRef)
   {
+    if (NS_FAILED(mStatus)) {
+      return *this;
+    }
+    mStatus = mMutator->SetRef(aRef, nullptr);
     NS_ENSURE_SUCCESS(mStatus, *this);
-    mStatus = mMutator->SetRef(aRef, nullptr);
     return *this;
   }
   NS_MutateURI& SetFilePath(const nsACString& aFilePath)
   {
+    if (NS_FAILED(mStatus)) {
+      return *this;
+    }
+    mStatus = mMutator->SetFilePath(aFilePath, nullptr);
     NS_ENSURE_SUCCESS(mStatus, *this);
-    mStatus = mMutator->SetFilePath(aFilePath, nullptr);
     return *this;
   }
   NS_MutateURI& SetQuery(const nsACString& aQuery)
   {
+    if (NS_FAILED(mStatus)) {
+      return *this;
+    }
+    mStatus = mMutator->SetQuery(aQuery, nullptr);
     NS_ENSURE_SUCCESS(mStatus, *this);
-    mStatus = mMutator->SetQuery(aQuery, nullptr);
     return *this;
   }
   NS_MutateURI& SetQueryWithEncoding(const nsACString& query, const mozilla::Encoding *encoding)
   {
+    if (NS_FAILED(mStatus)) {
+      return *this;
+    }
+    mStatus = mMutator->SetQueryWithEncoding(query, encoding, nullptr);
     NS_ENSURE_SUCCESS(mStatus, *this);
-    mStatus = mMutator->SetQueryWithEncoding(query, encoding, nullptr);
     return *this;
   }
 
   /**
    * This method allows consumers to call the methods declared in other
    * interfaces implemented by the mutator object.
    *
    * Example:
@@ -409,17 +449,19 @@ public:
    *
    * If mMutator does not implement SomeInterface, do_QueryInterface will fail
    * and the method will not be called.
    * If aMethod does not exist, or if there is a mismatch between argument
    * types, or the number of arguments, then there will be a compile error.
    */
   NS_MutateURI& Apply(const std::function<nsresult(nsIURIMutator*)>& aFunction)
   {
-    NS_ENSURE_SUCCESS(mStatus, *this);
+    if (NS_FAILED(mStatus)) {
+      return *this;
+    }
     mStatus = aFunction(mMutator);
     NS_ENSURE_SUCCESS(mStatus, *this);
     return *this;
   }
 
   template <class C>
   MOZ_MUST_USE nsresult Finalize(nsCOMPtr<C>& aURI)
   {

--- a/netwerk/base/nsIURIMutatorUtils.cpp
+++ b/netwerk/base/nsIURIMutatorUtils.cpp
@@ -9,15 +9,16 @@ GetURIMutator(nsIURI* aURI, nsIURIMutato
         return NS_ERROR_INVALID_ARG;
     }
     return aURI->Mutate(aMutator);
 }
 
 NS_MutateURI::NS_MutateURI(nsIURI* aURI)
 {
   mStatus = GetURIMutator(aURI, getter_AddRefs(mMutator));
+  NS_ENSURE_SUCCESS_VOID(mStatus);
 }
 
 NS_MutateURI::NS_MutateURI(const char * aContractID)
 {
   mMutator = do_CreateInstance(aContractID, &mStatus);
   MOZ_ASSERT(NS_SUCCEEDED(mStatus), "Called with wrong aContractID");
 }