Ok, apparently the controller isn't working on the web. I'm investigating.
Why the controller doesn't work automatically in Chrome but does so in FF is still unknown, especially since I'm using the same controller code from a previous project that does work. I have added a manual fix. Press "J" to bring up a prompt. It'll ask you to press a button on the controller you wish to use. Once it says it was detected, press J again to close the prompt then start the game normally.