Sets Firefox/Thunderbird Locale to Windows (MUI) Language on startup. This is most useful in Multi-Language Environment. If you install fx/tb language packs for languages that are installed on the OS, the app language follows automatically. This behavior can be overridden, if the user selects the language explicitly with the "locale switcher" extension.
Firefox 5.0 and later, Thunderbird 5.0 and later
Adjusted the restartApp() function. Didn't work after FF 45.x.