Fatal Error activating on WP 4.7 sites.

Plugin could not be activated because it triggered a fatal error.

Fatal error: Uncaught Error: Class 'Mozilla\WP_SW_Manager' not found in /home/xxxxx/public_html/wp-content/plugins/offline-content/class-wp-offline-content-plugin.php:31 Stack trace: #0 /home/xxxxxxx/public_html/wp-content/plugins/offline-content/class-wp-offline-content-plugin.php(21): WP_Offline_Content_Plugin->setup_sw() #1 /home/xxxxxxx/public_html/wp-content/plugins/offline-content/class-wp-offline-content-plugin.php(10): WP_Offline_Content_Plugin->__construct() #2 /home/xxxxxx/public_html/wp-content/plugins/offline-content/wp-offline-content.php(22): WP_Offline_Content_Plugin::init() #3 /home/xxxxxx/public_html/wp-admin/includes/plugin.php(1882): include('/home/xxxxxx/...') #4 /home/xxxxxx/public_html/wp-admin/plugins.php(164): plugin_sandbox_scrape('offline-content...') #5 {main} thrown in /home/xxxxx/public_html/wp-content/plugins/offline-content/class-wp-offline-content-plugin.php on line 31

This has happened on multiple sites running WP 4.7.