Since the latest update on Mozilla, you can't run WebGL offline from your desktop PC or laptop. But don't worry, we have a fix for you. First, you need to open your Mozilla browser and go to "about:config". After clicking the "Accept the Risk and Continue" button, you should see the option "webgl.disabled" at the top. By default, it's set to "true", which means WebGL will not work. However, if you click on the button next to "true", it will change to "false". After this, you should test your game offline on the desktop before submitting it to gamemonetize.com. Here is a video demonstrating how to do it:

In case it still does not work, then try the old version of Mozilla from here.