I probably should have included a "restart" button along with the save window, but there should still be a few simple ways to do go back to the beginning
Opening the game in a new browser tab/window should bring you back to the beginning (with any previous save data still hopefully intact in the save slots).
Clearing browser cookies should get rid of your save data if you just want to start fresh.
And the kinda brute-force option is just to get to a "Game Over", which prompts you to return to the title menu. Easiest way to do this is likely trying to cross the Brinebog without a guide.
Hope this helps!