diff --git a/dom/plugins/base/nsJSNPRuntime.cpp b/dom/plugins/base/nsJSNPRuntime.cpp
index 6debf2bef339a5..0b62c3b828af10 100644
--- a/dom/plugins/base/nsJSNPRuntime.cpp
+++ b/dom/plugins/base/nsJSNPRuntime.cpp
@@ -15,6 +15,7 @@
 #include "nsIScriptGlobalObject.h"
 #include "nsIScriptContext.h"
 #include "nsDOMJSUtils.h"
+#include "nsJSUtils.h"
 #include "nsCxPusher.h"
 #include "nsIDocument.h"
 #include "nsIJSRuntimeService.h"
@@ -405,13 +406,11 @@ JSValToNPVariant(NPP npp, JSContext *cx, JS::Value val, NPVariant *variant)
       }
     } else if (val.isString()) {
       JSString *jsstr = val.toString();
-      size_t length;
-      const jschar *chars = ::JS_GetStringCharsZAndLength(cx, jsstr, &length);
-      if (!chars) {
-          return false;
-      }
 
-      nsDependentString str(chars, length);
+      nsAutoJSString str;
+      if (!str.init(cx, jsstr)) {
+        return false;
+      }
 
       uint32_t len;
       char *p = ToNewUTF8String(str, &len);
diff --git a/js/ipc/JavaScriptShared.cpp b/js/ipc/JavaScriptShared.cpp
index 9d5b3de2046323..b048d8e3e3673e 100644
--- a/js/ipc/JavaScriptShared.cpp
+++ b/js/ipc/JavaScriptShared.cpp
@@ -201,12 +201,7 @@ JavaScriptShared::convertIdToGeckoString(JSContext *cx, JS::HandleId id, nsStrin
     if (!str)
         return false;
 
-    const jschar *chars = JS_GetStringCharsZ(cx, str);
-    if (!chars)
-        return false;
-
-    *to = chars;
-    return true;
+    return AssignJSString(cx, *to, str);
 }
 
 bool
diff --git a/storage/src/mozStorageAsyncStatementParams.cpp b/storage/src/mozStorageAsyncStatementParams.cpp
index 882f1d062b51d3..f88063dc8d3f73 100644
--- a/storage/src/mozStorageAsyncStatementParams.cpp
+++ b/storage/src/mozStorageAsyncStatementParams.cpp
@@ -7,6 +7,7 @@
 #include "nsMemory.h"
 #include "nsString.h"
 #include "nsCOMPtr.h"
+#include "nsJSUtils.h"
 
 #include "jsapi.h"
 
@@ -65,9 +66,12 @@ AsyncStatementParams::SetProperty(
   }
   else if (JSID_IS_STRING(aId)) {
     JSString *str = JSID_TO_STRING(aId);
-    size_t length;
-    const jschar *chars = JS_GetInternedStringCharsAndLength(str, &length);
-    NS_ConvertUTF16toUTF8 name(chars, length);
+    nsAutoJSString autoStr;
+    if (!autoStr.init(aCtx, str)) {
+      return NS_ERROR_FAILURE;
+    }
+
+    NS_ConvertUTF16toUTF8 name(autoStr);
 
     nsCOMPtr<nsIVariant> variant(convertJSValToVariant(aCtx, *_vp));
     NS_ENSURE_TRUE(variant, NS_ERROR_UNEXPECTED);
diff --git a/storage/src/mozStorageStatementParams.cpp b/storage/src/mozStorageStatementParams.cpp
index d661733323aa96..3d1d2466acc528 100644
--- a/storage/src/mozStorageStatementParams.cpp
+++ b/storage/src/mozStorageStatementParams.cpp
@@ -4,6 +4,7 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
+#include "nsJSUtils.h"
 #include "nsMemory.h"
 #include "nsString.h"
 
@@ -63,10 +64,12 @@ StatementParams::SetProperty(nsIXPConnectWrappedNative *aWrapper,
   }
   else if (JSID_IS_STRING(aId)) {
     JSString *str = JSID_TO_STRING(aId);
-    size_t length;
-    const jschar *chars = JS_GetStringCharsAndLength(aCtx, str, &length);
-    NS_ENSURE_TRUE(chars, NS_ERROR_UNEXPECTED);
-    NS_ConvertUTF16toUTF8 name(chars, length);
+    nsAutoJSString autoStr;
+    if (!autoStr.init(aCtx, str)) {
+      return NS_ERROR_FAILURE;
+    }
+
+    NS_ConvertUTF16toUTF8 name(autoStr);
 
     // check to see if there's a parameter with this name
     nsCOMPtr<nsIVariant> variant(convertJSValToVariant(aCtx, *_vp));
@@ -182,13 +185,14 @@ StatementParams::NewResolve(nsIXPConnectWrappedNative *aWrapper,
   }
   else if (JSID_IS_STRING(id)) {
     JSString *str = JSID_TO_STRING(id);
-    size_t nameLength;
-    const jschar *nameChars = JS_GetStringCharsAndLength(aCtx, str, &nameLength);
-    NS_ENSURE_TRUE(nameChars, NS_ERROR_UNEXPECTED);
+    nsAutoJSString autoStr;
+    if (!autoStr.init(aCtx, str)) {
+      return NS_ERROR_FAILURE;
+    }
 
     // Check to see if there's a parameter with this name, and if not, let
     // the rest of the prototype chain be checked.
-    NS_ConvertUTF16toUTF8 name(nameChars, nameLength);
+    NS_ConvertUTF16toUTF8 name(autoStr);
     uint32_t idx;
     nsresult rv = mStatement->GetParameterIndex(name, &idx);
     if (NS_SUCCEEDED(rv)) {
diff --git a/toolkit/components/places/History.cpp b/toolkit/components/places/History.cpp
index d58936e3d36066..7fd88a94fa0475 100644
--- a/toolkit/components/places/History.cpp
+++ b/toolkit/components/places/History.cpp
@@ -31,6 +31,7 @@
 #include "nsIXPConnect.h"
 #include "mozilla/unused.h"
 #include "nsContentUtils.h" // for nsAutoScriptBlocker
+#include "nsJSUtils.h"
 #include "mozilla/ipc/URIUtils.h"
 #include "nsPrintfCString.h"
 #include "nsTHashtable.h"
@@ -326,14 +327,10 @@ GetJSValueAsString(JSContext* aCtx,
     _string.Truncate();
     return;
   }
-  size_t length;
-  const jschar* chars =
-    JS_GetStringCharsZAndLength(aCtx, aValue.toString(), &length);
-  if (!chars) {
+
+  if (!AssignJSString(aCtx, _string, aValue.toString())) {
     _string.SetIsVoid(true);
-    return;
   }
-  _string.Assign(static_cast<const char16_t*>(chars), length);
 }
 
 /**
diff --git a/widget/android/NativeJSContainer.cpp b/widget/android/NativeJSContainer.cpp
index c41b81c2c2d5fd..1c4d7e13cb7743 100644
--- a/widget/android/NativeJSContainer.cpp
+++ b/widget/android/NativeJSContainer.cpp
@@ -7,6 +7,7 @@
 #include "AndroidBridge.h"
 #include "mozilla/Vector.h"
 #include "prthread.h"
+#include "nsJSUtils.h"
 
 using namespace mozilla;
 using namespace mozilla::widget;
@@ -502,14 +503,11 @@ struct StringProperty
 
     static Type FromValue(JNIEnv* env, jobject instance,
                           JSContext* cx, const JS::HandleString str) {
-        size_t strLen = 0;
-        const jschar* const strChars =
-            JS_GetStringCharsAndLength(cx, str, &strLen);
-        if (!CheckJSCall(env, !!strChars)) {
+        nsAutoJSString autoStr;
+        if (!CheckJSCall(env, autoStr.init(cx, str))) {
             return nullptr;
         }
-        jstring ret = env->NewString(
-            reinterpret_cast<const jchar*>(strChars), strLen);
+        jstring ret = env->NewString(autoStr.BeginReading(), autoStr.Length());
         MOZ_ASSERT(ret);
         return ret;
     }