If you're playing a game from a website there's chances you'll lose the data. I downloaded the game. It has a save file on your pc. It's probably a good idea to not depend on web based save files.
I have yet to lose my progress on pc and you can also backup the file if you want. It's in the form of a .dat file. It sits in the same directory as the game exe.
As a way of caution I usually avoid browser based games. I would rather just download it. You have more control that way.