I don't have any GameMaker experience, but I have made a few small web browser games in Unity. Once your game is finished, adapting it into a web browser game is pretty much as simple as selecting WebGL as build platform, zipping up the resulting folder, and uploading it here on itch.io. To my understanding it uses Mozilla's technology to build for WebGL, so it works perfectly in Firefox. It can be kinda buggy in Chrome, and doesn't work at all in Internet Explorer. I'm not sure if GameMaker works well in those browsers or not.
I hope this helped some. Good luck in your game jam!