A recent update to Firefox added in a new suite of security features, one of which is preventing websites from passing your information back and forth. This might cause issues with certain modules that you may use while doing your classwork, including Labster online laboratories.
To prevent or repair issues relating to this, you can turn off this feature by clicking on the Application Menu on the top right of your screen and clicking Settings.
After, click on the Privacy and Security tab on the left side, and set your Browser Privacy policy to at least have Tracking Content set to 'Only in Private Windows.' The rest of the settings are up to you, but changing this setting will fix any cross-site issues you may have while browsing your course.