I am getting the below error with 3.33 and trying to use Mobile Frontend with the following setup:
wfLoadExtension( 'MobileFrontend' );
$wgMFAutodetectMobileView = true;
$wgMFDefaultSkinClass = 'SkinVector'; // use Vector skin
MediaWiki internal error.
Original exception: [e21caa824241ba159b043d0d] /Main_Page ConfigException from line 53 of /var/www/gwart.co.uk/mediawiki/includes/config/GlobalVarConfig.php: GlobalVarConfig::get: undefined option: 'ResourceLoaderLESSVars'
Backtrace:
#0 /var/www/gwart.co.uk/mediawiki/extensions/MobileFrontend/includes/MobileFrontend.hooks.php(707): GlobalVarConfig->get(string)
#1 /var/www/gwart.co.uk/mediawiki/includes/Hooks.php(174): MobileFrontendHooks::onBeforePageDisplay(OutputPage, SkinVector)
#2 /var/www/gwart.co.uk/mediawiki/includes/Hooks.php(234): Hooks::callHook(string, array, array, NULL, string)
#3 /var/www/gwart.co.uk/mediawiki/includes/OutputPage.php(2711): Hooks::runWithoutAbort(string, array)
#4 /var/www/gwart.co.uk/mediawiki/includes/MediaWiki.php(869): OutputPage->output(boolean)
#5 /var/www/gwart.co.uk/mediawiki/includes/MediaWiki.php(881): MediaWiki->{closure}()
#6 /var/www/gwart.co.uk/mediawiki/includes/MediaWiki.php(517): MediaWiki->main()
#7 /var/www/gwart.co.uk/mediawiki/index.php(42): MediaWiki->run()
#8 {main}
Exception caught inside exception handler: [e21caa824241ba159b043d0d] /Main_Page ConfigException from line 53 of /var/www/gwart.co.uk/mediawiki/includes/config/GlobalVarConfig.php: GlobalVarConfig::get: undefined option: 'ResourceLoaderLESSVars'
Backtrace:
#0 /var/www/gwart.co.uk/mediawiki/extensions/MobileFrontend/includes/MobileFrontend.hooks.php(707): GlobalVarConfig->get(string)
#1 /var/www/gwart.co.uk/mediawiki/includes/Hooks.php(174): MobileFrontendHooks::onBeforePageDisplay(OutputPage, SkinVector)
#2 /var/www/gwart.co.uk/mediawiki/includes/Hooks.php(234): Hooks::callHook(string, array, array, NULL, string)
#3 /var/www/gwart.co.uk/mediawiki/includes/OutputPage.php(2711): Hooks::runWithoutAbort(string, array)
#4 /var/www/gwart.co.uk/mediawiki/includes/exception/MWExceptionRenderer.php(136): OutputPage->output()
#5 /var/www/gwart.co.uk/mediawiki/includes/exception/MWExceptionRenderer.php(53): MWExceptionRenderer::reportHTML(ConfigException)
#6 /var/www/gwart.co.uk/mediawiki/includes/exception/MWExceptionHandler.php(98): MWExceptionRenderer::output(ConfigException, integer)
#7 /var/www/gwart.co.uk/mediawiki/includes/exception/MWExceptionHandler.php(172): MWExceptionHandler::report(ConfigException)
#8 /var/www/gwart.co.uk/mediawiki/includes/MediaWiki.php(544): MWExceptionHandler::handleException(ConfigException)
#9 /var/www/gwart.co.uk/mediawiki/index.php(42): MediaWiki->run()
#10 {main}