diff --git a/dom/base/nsContentUtils.cpp b/dom/base/nsContentUtils.cpp
index 4b94e19153a5..282ca4acda00 100644
--- a/dom/base/nsContentUtils.cpp
+++ b/dom/base/nsContentUtils.cpp
@@ -10992,7 +10992,7 @@ template <prototypes::ID PrototypeID, class NativeType, typename T>
 static Result<Ok, nsresult>
 ExtractExceptionValues(JSContext* aCx,
                        JS::HandleObject aObj,
-                       nsACString& aSourceSpecOut,
+                       nsAString& aSourceSpecOut,
                        uint32_t* aLineOut,
                        uint32_t* aColumnOut,
                        nsString& aMessageOut)
@@ -11000,10 +11000,8 @@ ExtractExceptionValues(JSContext* aCx,
   RefPtr<T> exn;
   MOZ_TRY((UnwrapObject<PrototypeID, NativeType>(aObj, exn)));
 
-  nsAutoString filename;
-  exn->GetFilename(aCx, filename);
-  if (!filename.IsEmpty()) {
-    CopyUTF16toUTF8(filename, aSourceSpecOut);
+  exn->GetFilename(aCx, aSourceSpecOut);
+  if (!aSourceSpecOut.IsEmpty()) {
     *aLineOut = exn->LineNumber(aCx);
     *aColumnOut = exn->ColumnNumber();
   }
@@ -11024,6 +11022,19 @@ nsContentUtils::ExtractErrorValues(JSContext* aCx,
                                    uint32_t* aLineOut,
                                    uint32_t* aColumnOut,
                                    nsString& aMessageOut)
+{
+  nsAutoString sourceSpec;
+  ExtractErrorValues(aCx, aValue, sourceSpec, aLineOut, aColumnOut, aMessageOut);
+  CopyUTF16toUTF8(sourceSpec, aSourceSpecOut);
+}
+
+/* static */ void
+nsContentUtils::ExtractErrorValues(JSContext* aCx,
+                                   JS::Handle<JS::Value> aValue,
+                                   nsAString& aSourceSpecOut,
+                                   uint32_t* aLineOut,
+                                   uint32_t* aColumnOut,
+                                   nsString& aMessageOut)
 {
   MOZ_ASSERT(aLineOut);
   MOZ_ASSERT(aColumnOut);
@@ -11045,7 +11056,7 @@ nsContentUtils::ExtractErrorValues(JSContext* aCx,
                    0);          // window ID
 
       if (!report->mFileName.IsEmpty()) {
-        CopyUTF16toUTF8(report->mFileName, aSourceSpecOut);
+        aSourceSpecOut = report->mFileName;
         *aLineOut = report->mLineNumber;
         *aColumnOut = report->mColumn;
       }
diff --git a/dom/base/nsContentUtils.h b/dom/base/nsContentUtils.h
index 83d3974d32a9..601e7c121f24 100644
--- a/dom/base/nsContentUtils.h
+++ b/dom/base/nsContentUtils.h
@@ -1134,6 +1134,14 @@ public:
 
   static bool PrefetchPreloadEnabled(nsIDocShell* aDocShell);
 
+  static void
+  ExtractErrorValues(JSContext* aCx, JS::Handle<JS::Value> aValue,
+                     nsAString& aSourceSpecOut, uint32_t *aLineOut,
+                     uint32_t *aColumnOut, nsString& aMessageOut);
+
+  // Variant on `ExtractErrorValues` with a `nsACString`. This
+  // method is provided for backwards compatibility. Prefer the
+  // faster method above for your code.
   static void
   ExtractErrorValues(JSContext* aCx, JS::Handle<JS::Value> aValue,
                      nsACString& aSourceSpecOut, uint32_t *aLineOut,