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).
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Bartosz Dziewoński