Sorry about that. These three steps resolve the problem in the majority of cases.
1. Update your browser to the latest version
We suggest having the most recent versions of one or more of the following browsers: Chrome, Firefox, or Safari.
2. Clear your brower's cache
Clear your browser's cache and restart the browser. Also try loading the site in a second browser to see if it works.
3. Test that your plugins are up-to-date
Check that all of your plugins are up-to-date: www.mozilla.org/en-US/plugincheck/ (Note that you don't need to have Flash installed to use Codecademy.)
If you're still having trouble after following these three steps, please reach out to us.