Bug 41966: Allow removing locales from the locale alternatives list.

browser/components/preferences/dialogs/browserLanguages.js

@@ -349,7 +349,7 @@ async function getLocaleDisplayInfo(localeCodes) {
       id: "locale-" + code,
       label: localeNames[i],
       value: code,
-      canRemove: !packagedLocales.has(code),
+      canRemove: code !== Services.locale.defaultLocale,
       installed: availableLocales.has(code),
     };
   });