You might just be zoomed in. That's a sticky setting on Firefox -- I keep it zoomed one or two steps up on Firefox for comfortable reading, and the demo didn't

You might just be zoomed in. That's a sticky setting on Firefox -- I keep it zoomed one or two steps up on Firefox for comfortable reading, and the demo didn't quite fit on my screen. Return to default zoom (Ctrl/Cmd+0) and it works fine.