Labster currently support Google Chrome and Firefox browsers. If you need assistance loading labs, consult the guide below:
https://help.labster.com/students/collections/2286564/sections/3094204/articles/3944461-basic-labster-troubleshooting/

If you are still having issues with labs after consulting the article above, please reach out to Labster support here for further assistance. 
https://help.labster.com/students/collections/681721/articles/1391733-contact-labster-support/#teacher-support