As there are no specified or created functions for GameMaker Studio that supports HTML5 networking, you would have to create your own extension and create your own server.

In this course I walk through all the steps to build a multiplayer HTML5 game in GameMaker: Studio

Using this knowledge will allow you not only make HTML5 games, but make a variety of applications that differ from games.

Having the power to make multiplayer games in the browser will open up a bridge of opportunities.

Make great games, be a great developer, and have a great time!