Thread:Project:Support desk/ Fatal error:Call to undefined function wfGetMainCache() ExtensionLoader.php/reply (3)

According to installation instructions at Extension:Gliffy, it seems that you could add  inside LocalSettings.php without the need of Extension Manager. But the Gliffy extension status isn't known to continue working on the latest MediaWiki version, so it may also fail. If that happens then you'll need to find another solution for that.