When Mootools is not being used on the frontend you can prevent loading by opening:
libraries/cms/html/behavior.php
At around line 63 you can wrap the Mootools loading statement as follows:
//if we are not using mootools on the frontend we can prevent it from being loaded if (Jfactory::getApplication()->isAdmin()) { JHtml::_('script', 'system/mootools-' . $type . '.js', array('version' => 'auto', 'relative' => true, 'detectDebug' => $debug)); }
//if we are not using mootools on the frontend we can prevent it from being loaded if (Jfactory::getApplication()->isAdmin()) { JHtml::_('script', 'system/mootools-' . $type . '.js', array('version' => 'auto', 'relative' => true, 'detectDebug' => $debug)); }