It looks like the current version of MobileFrontend requires PHP 5.5. The specific error you're getting is caused by a use of the ClassName::class syntax (https://wiki.php.net/rfc/class_name_scalars), there are probably other places where some new syntax is used.
Note that MediaWiki 1.27 will also require PHP 5.5 (https://www.mediawiki.org/wiki/Compatibility#PHP).