diff --git a/dom/base/nsContentUtils.cpp b/dom/base/nsContentUtils.cpp
index 2f4bdced37106..d2967dfe84dac 100644
--- a/dom/base/nsContentUtils.cpp
+++ b/dom/base/nsContentUtils.cpp
@@ -3724,7 +3724,7 @@ nsresult nsContentUtils::ReportToConsoleByWindowID(
     NS_ENSURE_SUCCESS(rv, rv);
   }
 
-  nsAutoCString spec;
+  nsAutoString spec;
   if (!aLineNumber && aLocationMode == eUSE_CALLING_LOCATION) {
     JSContext* cx = GetCurrentJSContext();
     if (cx) {
@@ -3737,11 +3737,10 @@ nsresult nsContentUtils::ReportToConsoleByWindowID(
   NS_ENSURE_SUCCESS(rv, rv);
 
   if (!spec.IsEmpty()) {
-    rv =
-        errorObject->InitWithWindowID(aErrorText,
-                                      NS_ConvertUTF8toUTF16(spec),  // file name
-                                      aSourceLine, aLineNumber, aColumnNumber,
-                                      aErrorFlags, aCategory, aInnerWindowID);
+    rv = errorObject->InitWithWindowID(aErrorText,
+                                       spec,  // file name
+                                       aSourceLine, aLineNumber, aColumnNumber,
+                                       aErrorFlags, aCategory, aInnerWindowID);
   } else {
     rv = errorObject->InitWithSourceURI(aErrorText, aURI, aSourceLine,
                                         aLineNumber, aColumnNumber, aErrorFlags,
diff --git a/dom/bindings/BindingUtils.cpp b/dom/bindings/BindingUtils.cpp
index 1974b1785daaa..b05f2daf92e25 100644
--- a/dom/bindings/BindingUtils.cpp
+++ b/dom/bindings/BindingUtils.cpp
@@ -4003,7 +4003,7 @@ void DeprecationWarning(const GlobalObject& aGlobal,
     if (window && window->GetExtantDoc()) {
       window->GetExtantDoc()->WarnOnceAbout(aOperation);
 
-      nsAutoCString fileName;
+      nsAutoString fileName;
       Nullable<uint32_t> lineNumber;
       Nullable<uint32_t> columnNumber;
       uint32_t line = 0;
@@ -4014,8 +4014,7 @@ void DeprecationWarning(const GlobalObject& aGlobal,
         columnNumber.SetValue(column);
       }
 
-      MaybeReportDeprecation(window, aOperation,
-                             NS_ConvertUTF8toUTF16(fileName), lineNumber,
+      MaybeReportDeprecation(window, aOperation, fileName, lineNumber,
                              columnNumber);
     }
 
diff --git a/dom/media/webaudio/WebAudioUtils.cpp b/dom/media/webaudio/WebAudioUtils.cpp
index 3107d0d64bf6c..4ededeb145285 100644
--- a/dom/media/webaudio/WebAudioUtils.cpp
+++ b/dom/media/webaudio/WebAudioUtils.cpp
@@ -110,7 +110,7 @@ void WebAudioUtils::LogToDeveloperConsole(uint64_t aWindowID,
     return;
   }
 
-  nsAutoCString spec;
+  nsAutoString spec;
   uint32_t aLineNumber, aColumnNumber;
   JSContext* cx = nsContentUtils::GetCurrentJSContext();
   if (cx) {
@@ -134,9 +134,9 @@ void WebAudioUtils::LogToDeveloperConsole(uint64_t aWindowID,
     return;
   }
 
-  errorObject->InitWithWindowID(
-      result, NS_ConvertUTF8toUTF16(spec), EmptyString(), aLineNumber,
-      aColumnNumber, nsIScriptError::warningFlag, "Web Audio", aWindowID);
+  errorObject->InitWithWindowID(result, spec, EmptyString(), aLineNumber,
+                                aColumnNumber, nsIScriptError::warningFlag,
+                                "Web Audio", aWindowID);
   console->LogMessage(errorObject);
 }
 
diff --git a/dom/security/featurepolicy/FeaturePolicyUtils.cpp b/dom/security/featurepolicy/FeaturePolicyUtils.cpp
index 20a0dfa147ec6..6b4e94f7a06e2 100644
--- a/dom/security/featurepolicy/FeaturePolicyUtils.cpp
+++ b/dom/security/featurepolicy/FeaturePolicyUtils.cpp
@@ -136,7 +136,7 @@ void FeaturePolicyUtils::ReportViolation(Document* aDocument,
     return;
   }
 
-  nsAutoCString fileName;
+  nsAutoString fileName;
   Nullable<int32_t> lineNumber;
   Nullable<int32_t> columnNumber;
   uint32_t line = 0;
@@ -152,9 +152,9 @@ void FeaturePolicyUtils::ReportViolation(Document* aDocument,
   }
 
   RefPtr<FeaturePolicyViolationReportBody> body =
-      new FeaturePolicyViolationReportBody(
-          window, aFeatureName, NS_ConvertUTF8toUTF16(fileName), lineNumber,
-          columnNumber, NS_LITERAL_STRING("enforce"));
+      new FeaturePolicyViolationReportBody(window, aFeatureName, fileName,
+                                           lineNumber, columnNumber,
+                                           NS_LITERAL_STRING("enforce"));
 
   ReportingUtils::Report(window, nsGkAtoms::featurePolicyViolation,
                          NS_LITERAL_STRING("default"),
diff --git a/dom/security/nsCSPContext.cpp b/dom/security/nsCSPContext.cpp
index 33ff6887c20e5..0df8d69010be6 100644
--- a/dom/security/nsCSPContext.cpp
+++ b/dom/security/nsCSPContext.cpp
@@ -213,7 +213,7 @@ bool nsCSPContext::permitsInternal(
       if (!aIsPreload && aSendViolationReports) {
         uint32_t lineNumber = 0;
         uint32_t columnNumber = 0;
-        nsAutoCString spec;
+        nsAutoString spec;
         JSContext* cx = nsContentUtils::GetCurrentJSContext();
         if (cx) {
           nsJSUtils::GetCallingLocation(cx, spec, &lineNumber, &columnNumber);
@@ -229,10 +229,10 @@ bool nsCSPContext::permitsInternal(
                                        null */
             violatedDirective, p,   /* policy index        */
             EmptyString(),          /* no observer subject */
-            NS_ConvertUTF8toUTF16(spec), /* source file      */
-            EmptyString(),               /* no script sample    */
-            lineNumber,                  /* line number      */
-            columnNumber);               /*  column number    */
+            spec,                   /* source file      */
+            EmptyString(),          /* no script sample    */
+            lineNumber,             /* line number      */
+            columnNumber);          /*  column number    */
       }
     }
   }