You can right-click and choose "Save image as..." (or something similar) in most browsers! It'll export the whole dungeon, including the title and text at the top.
If you change toggle the notes off/on and repeat the image save, you can create a DM copy and a player copy!
That's super weird, I'm not sure why Firefox is just outputting an empty PNG. @watabou says below that he may add a proper export button in the future if he continues development, but in the meanwhile, you may need to install Chrome to save it without just taking a screenshot.
Surprisingly the method described by @alamantus doesn't work in Firefox, but you still can take a screenshot. If I decide to continue developing this generator, I'll add a proper export button.
