If I uninstall the 4.3 browser extension, disable automatic updating of extensions, quit Safari and after launching it again download the 4.2.5 extension available here it then works with the exact same Login items.
If I uninstall the 4.3 browser extension, disable automatic updating of extensions, quit Safari and after launching it again download the 4.2.5 extension available here it then works with the exact same Login items.