diff --git a/dom/bindings/BindingUtils.cpp b/dom/bindings/BindingUtils.cpp
index 9e2c1079c8d1..7bdf7960892f 100644
--- a/dom/bindings/BindingUtils.cpp
+++ b/dom/bindings/BindingUtils.cpp
@@ -54,8 +54,7 @@ JSErrorFormatString ErrorFormatString[] = {
 };
 
 const JSErrorFormatString*
-GetErrorMessage(void* aUserRef, const char* aLocale,
-                const unsigned aErrorNumber)
+GetErrorMessage(void* aUserRef, const unsigned aErrorNumber)
 {
   MOZ_ASSERT(aErrorNumber < ArrayLength(ErrorFormatString));
   return &ErrorFormatString[aErrorNumber];
@@ -139,8 +138,7 @@ ErrorResult::ThrowTypeError(const dom::ErrNum errorNumber, ...)
   mResult = NS_ERROR_TYPE_ERR;
   Message* message = new Message();
   message->mErrorNumber = errorNumber;
-  uint16_t argCount =
-    dom::GetErrorMessage(nullptr, nullptr, errorNumber)->argCount;
+  uint16_t argCount = dom::GetErrorMessage(nullptr, errorNumber)->argCount;
   MOZ_ASSERT(argCount <= 10);
   argCount = std::min<uint16_t>(argCount, 10);
   while (argCount--) {
diff --git a/js/src/ctypes/CTypes.cpp b/js/src/ctypes/CTypes.cpp
index da6e97a7cb86..4354e1b1bbf8 100644
--- a/js/src/ctypes/CTypes.cpp
+++ b/js/src/ctypes/CTypes.cpp
@@ -877,7 +877,7 @@ static const JSErrorFormatString ErrorFormatString[CTYPESERR_LIMIT] = {
 };
 
 static const JSErrorFormatString*
-GetErrorMessage(void* userRef, const char* locale, const unsigned errorNumber)
+GetErrorMessage(void* userRef, const unsigned errorNumber)
 {
   if (0 < errorNumber && errorNumber < CTYPESERR_LIMIT)
     return &ErrorFormatString[errorNumber];
diff --git a/js/src/jsapi.h b/js/src/jsapi.h
index c42aa76cfcf3..24226b102b4c 100644
--- a/js/src/jsapi.h
+++ b/js/src/jsapi.h
@@ -733,8 +733,7 @@ typedef struct JSErrorFormatString {
 } JSErrorFormatString;
 
 typedef const JSErrorFormatString *
-(* JSErrorCallback)(void *userRef, const char *locale,
-                    const unsigned errorNumber);
+(* JSErrorCallback)(void *userRef, const unsigned errorNumber);
 
 typedef bool
 (* JSLocaleToUpperCase)(JSContext *cx, JS::HandleString src, JS::MutableHandleValue rval);
@@ -4536,7 +4535,6 @@ struct JSLocaleCallbacks {
     JSLocaleToLowerCase     localeToLowerCase;
     JSLocaleCompare         localeCompare; // not used #if EXPOSE_INTL_API
     JSLocaleToUnicode       localeToUnicode;
-    JSErrorCallback         localeGetErrorMessage;
 };
 
 /*
diff --git a/js/src/jscntxt.cpp b/js/src/jscntxt.cpp
index 37e49c7c161c..9831da0cc081 100644
--- a/js/src/jscntxt.cpp
+++ b/js/src/jscntxt.cpp
@@ -391,8 +391,7 @@ js_ReportOutOfMemory(ThreadSafeContext *cxArg)
     }
 
     /* Get the message for this error, but we don't expand any arguments. */
-    const JSErrorFormatString *efs =
-        js_GetLocalizedErrorMessage(cx, nullptr, nullptr, JSMSG_OUT_OF_MEMORY);
+    const JSErrorFormatString *efs = js_GetErrorMessage(nullptr, JSMSG_OUT_OF_MEMORY);
     const char *msg = efs ? efs->format : "Out of memory";
 
     /* Fill out the report, but don't do anything that requires allocation. */
@@ -671,13 +670,14 @@ js_ExpandErrorArguments(ExclusiveContext *cx, JSErrorCallback callback,
 
     *messagep = nullptr;
 
-    /* Most calls supply js_GetErrorMessage; if this is so, assume nullptr. */
-    if (!callback || callback == js_GetErrorMessage) {
-        efs = js_GetLocalizedErrorMessage(cx, userRef, nullptr, errorNumber);
-    } else {
+    if (!callback)
+        callback = js_GetErrorMessage;
+
+    {
         AutoSuppressGC suppressGC(cx);
-        efs = callback(userRef, nullptr, errorNumber);
+        efs = callback(userRef, errorNumber);
     }
+
     if (efs) {
         reportp->exnType = efs->exnType;
 
@@ -1004,9 +1004,9 @@ const JSErrorFormatString js_ErrorFormatString[JSErr_Limit] = {
 };
 
 JS_FRIEND_API(const JSErrorFormatString *)
-js_GetErrorMessage(void *userRef, const char *locale, const unsigned errorNumber)
+js_GetErrorMessage(void *userRef, const unsigned errorNumber)
 {
-    if ((errorNumber > 0) && (errorNumber < JSErr_Limit))
+    if (errorNumber > 0 && errorNumber < JSErr_Limit)
         return &js_ErrorFormatString[errorNumber];
     return nullptr;
 }
diff --git a/js/src/jsexn.cpp b/js/src/jsexn.cpp
index fc1d2114a497..87dafb620278 100644
--- a/js/src/jsexn.cpp
+++ b/js/src/jsexn.cpp
@@ -579,28 +579,6 @@ ErrorObject::createConstructor(JSContext *cx, JSProtoKey key)
     return ctor;
 }
 
-const JSErrorFormatString*
-js_GetLocalizedErrorMessage(ExclusiveContext *cx, void *userRef, const char *locale,
-                            const unsigned errorNumber)
-{
-    const JSErrorFormatString *errorString = nullptr;
-
-    // The locale callbacks might not be thread safe, so don't call them if
-    // we're not on the main thread. When used with XPConnect,
-    // |localeGetErrorMessage| will be nullptr anyways.
-    if (cx->isJSContext() &&
-        cx->asJSContext()->runtime()->localeCallbacks &&
-        cx->asJSContext()->runtime()->localeCallbacks->localeGetErrorMessage)
-    {
-        JSLocaleCallbacks *callbacks = cx->asJSContext()->runtime()->localeCallbacks;
-        errorString = callbacks->localeGetErrorMessage(userRef, locale, errorNumber);
-    }
-
-    if (!errorString)
-        errorString = js_GetErrorMessage(userRef, locale, errorNumber);
-    return errorString;
-}
-
 JS_FRIEND_API(JSFlatString *)
 js::GetErrorTypeName(JSRuntime *rt, int16_t exnType)
 {
@@ -628,11 +606,9 @@ js_ErrorToException(JSContext *cx, const char *message, JSErrorReport *reportp,
 
     // Find the exception index associated with this error.
     JSErrNum errorNumber = static_cast<JSErrNum>(reportp->errorNumber);
-    const JSErrorFormatString *errorString;
-    if (!callback || callback == js_GetErrorMessage)
-        errorString = js_GetLocalizedErrorMessage(cx, nullptr, nullptr, errorNumber);
-    else
-        errorString = callback(userRef, nullptr, errorNumber);
+    if (!callback)
+        callback = js_GetErrorMessage;
+    const JSErrorFormatString *errorString = callback(userRef, errorNumber);
     JSExnType exnType = errorString ? static_cast<JSExnType>(errorString->exnType) : JSEXN_NONE;
     MOZ_ASSERT(exnType < JSEXN_LIMIT);
 
diff --git a/js/src/jsexn.h b/js/src/jsexn.h
index a56eeecb3aa5..858df5187eca 100644
--- a/js/src/jsexn.h
+++ b/js/src/jsexn.h
@@ -76,10 +76,6 @@ js_ReportUncaughtException(JSContext *cx);
 extern JSErrorReport *
 js_ErrorFromException(JSContext *cx, js::HandleObject obj);
 
-extern const JSErrorFormatString *
-js_GetLocalizedErrorMessage(js::ExclusiveContext *cx, void *userRef, const char *locale,
-                            const unsigned errorNumber);
-
 /*
  * Make a copy of errobj parented to cx's compartment's global.
  *
diff --git a/js/src/jsfriendapi.h b/js/src/jsfriendapi.h
index e22cb9e5bda3..d4ed1a5afca6 100644
--- a/js/src/jsfriendapi.h
+++ b/js/src/jsfriendapi.h
@@ -1242,7 +1242,7 @@ typedef enum JSErrNum {
 } JSErrNum;
 
 extern JS_FRIEND_API(const JSErrorFormatString *)
-js_GetErrorMessage(void *userRef, const char *locale, const unsigned errorNumber);
+js_GetErrorMessage(void *userRef, const unsigned errorNumber);
 
 namespace js {
 
diff --git a/js/src/shell/js.cpp b/js/src/shell/js.cpp
index 94d43f5f140c..83def21c8d24 100644
--- a/js/src/shell/js.cpp
+++ b/js/src/shell/js.cpp
@@ -198,7 +198,7 @@ NewGlobalObject(JSContext *cx, JS::CompartmentOptions &options,
                 JSPrincipals *principals);
 
 static const JSErrorFormatString *
-my_GetErrorMessage(void *userRef, const char *locale, const unsigned errorNumber);
+my_GetErrorMessage(void *userRef, const unsigned errorNumber);
 
 
 /*
@@ -5115,7 +5115,7 @@ static const JSErrorFormatString jsShell_ErrorFormatString[JSShellErr_Limit] = {
 };
 
 static const JSErrorFormatString *
-my_GetErrorMessage(void *userRef, const char *locale, const unsigned errorNumber)
+my_GetErrorMessage(void *userRef, const unsigned errorNumber)
 {
     if (errorNumber == 0 || errorNumber >= JSShellErr_Limit)
         return nullptr;
diff --git a/js/src/vm/SelfHosting.cpp b/js/src/vm/SelfHosting.cpp
index e2a280553d77..14331b67ba70 100644
--- a/js/src/vm/SelfHosting.cpp
+++ b/js/src/vm/SelfHosting.cpp
@@ -120,8 +120,7 @@ js::intrinsic_ThrowError(JSContext *cx, unsigned argc, Value *vp)
     uint32_t errorNumber = args[0].toInt32();
 
 #ifdef DEBUG
-    const JSErrorFormatString *efs =
-        js_GetLocalizedErrorMessage(cx, nullptr, nullptr, errorNumber);
+    const JSErrorFormatString *efs = js_GetErrorMessage(nullptr, errorNumber);
     JS_ASSERT(efs->argCount == args.length() - 1);
 #endif
 
diff --git a/js/xpconnect/src/XPCLocale.cpp b/js/xpconnect/src/XPCLocale.cpp
index ca51f8370943..03ecd931e0c6 100644
--- a/js/xpconnect/src/XPCLocale.cpp
+++ b/js/xpconnect/src/XPCLocale.cpp
@@ -43,7 +43,6 @@ struct XPCLocaleCallbacks : public JSLocaleCallbacks
     localeToLowerCase = LocaleToLowerCase;
     localeCompare = LocaleCompare;
     localeToUnicode = LocaleToUnicode;
-    localeGetErrorMessage = nullptr;
   }
 
   ~XPCLocaleCallbacks()
diff --git a/js/xpconnect/src/XPCShellImpl.cpp b/js/xpconnect/src/XPCShellImpl.cpp
index 2d31748ce62b..1aa67a32e717 100644
--- a/js/xpconnect/src/XPCShellImpl.cpp
+++ b/js/xpconnect/src/XPCShellImpl.cpp
@@ -881,7 +881,7 @@ static const JSErrorFormatString jsShell_ErrorFormatString[JSShellErr_Limit] = {
 };
 
 static const JSErrorFormatString *
-my_GetErrorMessage(void *userRef, const char *locale, const unsigned errorNumber)
+my_GetErrorMessage(void *userRef, const unsigned errorNumber)
 {
     if (errorNumber == 0 || errorNumber >= JSShellErr_Limit)
         return nullptr;