This add-on is a great version of The Super Mario Retro game. The only personal problem I have with this extension is that only part of the screen shows when clicked.

Its a button that opens a window to a website with the game

ok

it's good but not offline and there is a lot of add popups

good

After you know the controls, it seems to work pretty well. It opens a new window outside of firefox on which it runs the game. You can play/pause and quicksave the game, edit the sound, and controls.