Click the blue Search for an edition for my community button
Search for "college park" you should get one result
Click the result
Click Load this edition
Click the blue Install Maryland Libraries Toolbar for Firefox button
Follow the prompts, including restarting Firefox
If all goes well you should see a little Maryland flag icon in your browser toolbar. Click the flag to use LibX. If you don't see the icon you can also open your Add-ons and find it under extensions (you shouldn't need to activate it but that's where you would do so)