I'm not aware that Firefox has an app for Samsung TV's. You're stuck with the apps that come with it or that you can download from the Samsung App-store.
If no good help comes here (wait a few days) go back to the shop and ask them to show how it works. But I think a keyboard will be a nice addition.
I'm a new smart tv user and have not been able to find a step by step guideline for using the web browser. I can access the browser which apparently has MSN as a default but I can not figure out how to access and use search or select features and change the browser to Firefox. Do I need a keyboard.
Any help would be appreciated.