If the game freezes, just click inside it (games can get unresponsive if you click elsewhere on the page).
Think outside the box as you plot the blocks' spots.Position blocks as they fall, matching 4 or more blocks of the same color to clear them. If the blocks pile up to the top of the screen, it's game over!
Left/Right/Down Arrow keys - To move.
Up Arrow key - To rotate block.
Space bar - To drop block.