If you installed dropbox, and have it running, you will have a dropbox folder in your user profile folder in windows. (in windows 8 it shows up under favorites)
In here should be a public folder.
Copy your entire game folder into the public folder.
Enter the game folder in your dropbox folder, right click the index.html file, and select "copy public link"
This public link can be used to play your game from a browser.