We use something called "DOM storage" to store information about the exercises you have done. It's not necessary for watching videos but must be enabled to do exercises.
If you have one of these browsers and are still getting a message to enable DOM storage, jump to one of the following sections to turn it on in your browser.
Type "about:config" in the address bar
Click "I'll be careful, I promise!"
Type "dom.storage.enabled" in the text box. Make sure it says "true" under "Value". Double click to toggle between true and false.
Select "Extras" -> "Internet Options" -> "Advanced" Tab -> Go to "Security" -> check "Enable DOM-Storage"
Select the wrench and the "Preferences"
Choose "Allow local data to be set (recommended"