Use the arrow keys or A and D to move left and right. Left-click to interact. Hold-shift to auto-loot or buy/sell a stack of items.
The rest of the controls can be found in-game. All of the controls can be customized from the Game Menu under Key Bindings.
Note: Some people reported a graphical slow-down after playing for too long. To fix this issue, save your game and refresh the page. Turning off effects from the settings might help too!