diff --git a/dom/file/nsHostObjectProtocolHandler.cpp b/dom/file/nsHostObjectProtocolHandler.cpp
index d69d0d7e6065..a3e2546b6ebf 100644
--- a/dom/file/nsHostObjectProtocolHandler.cpp
+++ b/dom/file/nsHostObjectProtocolHandler.cpp
@@ -892,20 +892,23 @@ nsHostObjectProtocolHandler::NewURI(const nsACString& aSpec,
 
   DataInfo* info = GetDataInfo(aSpec);
 
+  nsCOMPtr<nsIPrincipal> principal;
+  RefPtr<mozilla::dom::BlobImpl> blob;
+  if (info && info->mObjectType == DataInfo::eBlobImpl) {
+    MOZ_ASSERT(info->mBlobImpl);
+    principal = info->mPrincipal;
+    blob = info->mBlobImpl;
+  }
+
   nsCOMPtr<nsIURI> uri;
   rv = NS_MutateURI(new nsHostObjectURI::Mutator())
          .SetSpec(aSpec)
+         .Apply<nsIBlobURIMutator>(&nsIBlobURIMutator::SetBlobImpl, blob)
+         .Apply<nsIPrincipalURIMutator>(&nsIPrincipalURIMutator::SetPrincipal, principal)
          .Finalize(uri);
   NS_ENSURE_SUCCESS(rv, rv);
 
-  RefPtr<nsHostObjectURI> hostURI = static_cast<nsHostObjectURI*>(uri.get());
-  if (info && info->mObjectType == DataInfo::eBlobImpl) {
-    MOZ_ASSERT(info->mBlobImpl);
-    hostURI->mPrincipal = info->mPrincipal;
-    hostURI->mBlobImpl = info->mBlobImpl;
-  }
-
-  NS_TryToSetImmutable(hostURI);
+  NS_TryToSetImmutable(uri);
   uri.forget(aResult);
 
   if (info && info->mObjectType == DataInfo::eBlobImpl) {
diff --git a/dom/file/nsHostObjectURI.cpp b/dom/file/nsHostObjectURI.cpp
index 8be9f50eb8d6..9a84c3aa9b83 100644
--- a/dom/file/nsHostObjectURI.cpp
+++ b/dom/file/nsHostObjectURI.cpp
@@ -230,7 +230,7 @@ nsHostObjectURI::EqualsInternal(nsIURI* aOther,
   return NS_OK;
 }
 
-NS_IMPL_ISUPPORTS(nsHostObjectURI::Mutator, nsIURISetters, nsIURIMutator)
+NS_IMPL_ISUPPORTS(nsHostObjectURI::Mutator, nsIURISetters, nsIURIMutator, nsIBlobURIMutator, nsIPrincipalURIMutator)
 
 NS_IMETHODIMP
 nsHostObjectURI::Mutate(nsIURIMutator** aMutator)
diff --git a/dom/file/nsHostObjectURI.h b/dom/file/nsHostObjectURI.h
index 3a9a7b63aa47..c7e12680b28d 100644
--- a/dom/file/nsHostObjectURI.h
+++ b/dom/file/nsHostObjectURI.h
@@ -81,11 +81,33 @@ public:
   class Mutator
     : public nsIURIMutator
     , public BaseURIMutator<nsHostObjectURI>
+    , public nsIBlobURIMutator
+    , public nsIPrincipalURIMutator
   {
     NS_DECL_ISUPPORTS
     NS_FORWARD_SAFE_NSIURISETTERS_RET(mURI)
     NS_DEFINE_NSIMUTATOR_COMMON
 
+    MOZ_MUST_USE NS_IMETHOD
+    SetBlobImpl(mozilla::dom::BlobImpl *aBlobImpl) override
+    {
+        if (!mURI) {
+            return NS_ERROR_NULL_POINTER;
+        }
+        mURI->mBlobImpl = aBlobImpl;
+        return NS_OK;
+    }
+
+    MOZ_MUST_USE NS_IMETHOD
+    SetPrincipal(nsIPrincipal *aPrincipal) override
+    {
+        if (!mURI) {
+            return NS_ERROR_NULL_POINTER;
+        }
+        mURI->mPrincipal = aPrincipal;
+        return NS_OK;
+    }
+
     explicit Mutator() { }
   private:
     virtual ~Mutator() { }
diff --git a/netwerk/base/nsIURIMutator.idl b/netwerk/base/nsIURIMutator.idl
index 687a691a83c1..63e70187ee18 100644
--- a/netwerk/base/nsIURIMutator.idl
+++ b/netwerk/base/nsIURIMutator.idl
@@ -369,6 +369,32 @@ public:
     return *this;
   }
 
+  /**
+   * This method allows consumers to call the methods declared in other
+   * interfaces implemented by the mutator object.
+   *
+   * Example:
+   * nsCOMPtr<nsIURI> uri;
+   * nsresult rv = NS_MutateURI(new URIClass::Mutator())
+   *                 .SetSpec(aSpec)
+   *                 .Apply<SomeInterface>(&SomeInterface::Method, arg1, arg2)
+   *                 .Finalize(uri);
+   *
+   * 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.
+   */
+  template <typename Interface, typename Method, typename... Args>
+  NS_MutateURI& Apply(Method aMethod, Args ...aArgs)
+  {
+    NS_ENSURE_SUCCESS(mStatus, *this);
+    nsCOMPtr<Interface> target = do_QueryInterface(mMutator, &mStatus);
+    NS_ENSURE_SUCCESS(mStatus, *this);
+    mStatus = (target->*aMethod)(aArgs...);
+    return *this;
+  }
+
   template <class C>
   MOZ_MUST_USE nsresult Finalize(nsCOMPtr<C>& aURI)
   {
diff --git a/netwerk/base/nsIURIWithBlobImpl.idl b/netwerk/base/nsIURIWithBlobImpl.idl
index e76c12c7ed26..1a3832e4a57b 100644
--- a/netwerk/base/nsIURIWithBlobImpl.idl
+++ b/netwerk/base/nsIURIWithBlobImpl.idl
@@ -6,6 +6,15 @@
 
 interface nsIURI;
 
+%{C++
+namespace mozilla {
+namespace dom {
+  class BlobImpl;
+}}
+%}
+
+[ptr] native BlobImplPtr(mozilla::dom::BlobImpl);
+
 /**
  * nsIURIWithBlobImpl is implemented by URIs which are associated with a
  * specific BlobImpl.
@@ -18,3 +27,14 @@ interface nsIURIWithBlobImpl : nsISupports
      */
     readonly attribute nsISupports blobImpl;
 };
+
+[builtinclass, uuid(d3e8c9fa-ff07-47cc-90dc-0cc5445ddb59)]
+interface nsIBlobURIMutator : nsISupports
+{
+    /**
+     * Associates a blobImpl to the mutated URI.
+     * Would normally return nsIURIMutator, but since it only gets called
+     * from C++, there is no need for that.
+     */
+    [must_use, noscript] void setBlobImpl(in BlobImplPtr blobImpl);
+};
diff --git a/netwerk/base/nsIURIWithPrincipal.idl b/netwerk/base/nsIURIWithPrincipal.idl
index 912225c90972..bd130b2b5282 100644
--- a/netwerk/base/nsIURIWithPrincipal.idl
+++ b/netwerk/base/nsIURIWithPrincipal.idl
@@ -6,6 +6,7 @@
 
 interface nsIPrincipal;
 interface nsIURI;
+interface nsIURIMutator;
 
 /**
  * nsIURIWithPrincipal is implemented by URIs which are associated with a
@@ -25,3 +26,14 @@ interface nsIURIWithPrincipal : nsISupports
      */
     readonly attribute nsIURI principalUri;
 };
+
+[builtinclass, uuid(fa138a89-c76e-4b7f-95ec-c7b56ded5ef5)]
+interface nsIPrincipalURIMutator : nsISupports
+{
+    /**
+     * Associates a principal to the mutated URI.
+     * Would normally return nsIURIMutator, but since it only gets called
+     * from C++, there is no need for that.
+     */
+    [must_use, noscript] void setPrincipal(in nsIPrincipal aPrincipal);
+};