--- a/dom/base/nsGlobalWindow.cpp
+++ b/dom/base/nsGlobalWindow.cpp
@@ -11397,17 +11397,17 @@ nsGlobalWindow::Observe(nsISupports* aSu
     event->SetTrusted(true);
 
     bool dummy;
     return DispatchEvent(event, &dummy);
   }
 #endif // MOZ_B2G
 
   if (!nsCRT::strcmp(aTopic, NS_PREFBRANCH_PREFCHANGE_TOPIC_ID)) {
-    MOZ_ASSERT(!nsCRT::strcmp(NS_ConvertUTF16toUTF8(aData).get(), "intl.accept_languages"));
+    MOZ_ASSERT(!NS_strcmp(aData, MOZ_UTF16("intl.accept_languages")));
     MOZ_ASSERT(IsInnerWindow());
 
     // The user preferred languages have changed, we need to fire an event on
     // Window object and invalidate the cache for navigator.languages. It is
     // done for every change which can be a waste of cycles but those should be
     // fairly rare.
     // We MUST invalidate navigator.languages before sending the event in the
     // very likely situation where an event handler will try to read its value.

--- a/dom/devicestorage/nsDeviceStorage.cpp
+++ b/dom/devicestorage/nsDeviceStorage.cpp
@@ -4229,19 +4229,19 @@ nsDOMDeviceStorage::Observe(nsISupports 
   }
   if (!strcmp(aTopic, "disk-space-watcher")) {
     // 'disk-space-watcher' notifications are sent when there is a modification
     // of a file in a specific location while a low device storage situation
     // exists or after recovery of a low storage situation. For Firefox OS,
     // these notifications are specific for apps storage.
     nsRefPtr<DeviceStorageFile> file =
       new DeviceStorageFile(mStorageType, mStorageName);
-    if (!strcmp(NS_ConvertUTF16toUTF8(aData).get(), "full")) {
+    if (!NS_strcmp(aData, MOZ_UTF16("full"))) {
       Notify("low-disk-space", file);
-    } else if (!strcmp(NS_ConvertUTF16toUTF8(aData).get(), "free")) {
+    } else if (!NS_strcmp(aData, MOZ_UTF16("free"))) {
       Notify("available-disk-space", file);
     }
     return NS_OK;
   }
 
 #ifdef MOZ_WIDGET_GONK
   else if (!strcmp(aTopic, NS_VOLUME_STATE_CHANGED)) {
     // We invalidate the used space cache for the volume that actually changed

--- a/image/src/imgLoader.cpp
+++ b/image/src/imgLoader.cpp
@@ -1071,17 +1071,17 @@ imgLoader::RespectPrivacyNotifications()
   return NS_OK;
 }
 
 NS_IMETHODIMP
 imgLoader::Observe(nsISupports* aSubject, const char* aTopic, const char16_t* aData)
 {
   // We listen for pref change notifications...
   if (!strcmp(aTopic, NS_PREFBRANCH_PREFCHANGE_TOPIC_ID)) {
-    if (!strcmp(NS_ConvertUTF16toUTF8(aData).get(), "image.http.accept")) {
+    if (!NS_strcmp(aData, MOZ_UTF16("image.http.accept"))) {
       ReadAcceptHeaderPref();
     }
 
   } else if (strcmp(aTopic, "memory-pressure") == 0) {
     MinimizeCaches();
   } else if (strcmp(aTopic, "chrome-flush-skin-caches") == 0 ||
              strcmp(aTopic, "chrome-flush-caches") == 0) {
     MinimizeCaches();

--- a/rdf/datasource/src/nsLocalStore.cpp
+++ b/rdf/datasource/src/nsLocalStore.cpp
@@ -470,17 +470,17 @@ LocalStoreImpl::Observe(nsISupports *aSu
             if (remote)
                 remote->Flush();
         }
 
         // Create an in-memory datasource for use while we're
         // profile-less.
         mInner = do_CreateInstance(NS_RDF_DATASOURCE_CONTRACTID_PREFIX "in-memory-datasource");
 
-        if (!nsCRT::strcmp(NS_ConvertUTF16toUTF8(someData).get(), "shutdown-cleanse")) {
+        if (!NS_strcmp(someData, MOZ_UTF16("shutdown-cleanse"))) {
             nsCOMPtr<nsIFile> aFile;
             rv = NS_GetSpecialDirectory(NS_APP_LOCALSTORE_50_FILE, getter_AddRefs(aFile));
             if (NS_SUCCEEDED(rv))
                 rv = aFile->Remove(false);
         }
     }
     else if (!nsCRT::strcmp(aTopic, "profile-do-change")) {
         rv = LoadData();