"Game files" here refers to IWADs, e.g. .wl6 or .sod files.
ECWolf officially supports Wolfenstein 3D, Spear of Destiny, and
Super 3D Noah's Ark.
The recommended way of playing the game is in a fullscreen Chrome
window. This way the browser will not interrupt the game with its
hotkeys (e.g. Ctrl+W). Unfortunately, Firefox does not (yet) support
the Keyboard Lock API.
Only keyboard controls are supported. Possibly mouse if you select
the windowed mouse option and restart the game.
Emscripten seems to get confused when launching straight into
fullscreen mode, so this option has been overriden in this demo.
Also, enabling fullscreen while the windowed mouse option is enabled
seems to crash the game. Or if you enable the fullscreen option
twice in a row by using the Ctrl key (but not with Enter).