GamePad API isn't a very good name as it actually covers more than just gamepads. Gamepad API gives webpages access to inputs of many types of controllers. The Chromium engine that powers Chrome and Opera browsers access 3DMice via Raw Input. Apparently Mozilla doesn't have a Raw Input solution. I don't think Microsoft does either, though I haven't yet tried their new edge browser.
As Utash mentioned 3DConnexion has a config for Chrome that let you control functions that the 2D Mouse typically controls. What would be nice is being able to somehow switch modes:
-one to zoom/pan the browser content window
-another to give input to the web app
Earlier this year I put all 6 axis to good use in Cesium
https://groups.google.com/forum/#!topic ... HEkXPyLKQw
You can try it out for yourself here (with a Chrome or Opera browser.) If you have an active Chrome config you should probably disable it while you're controlling the camera.
http://warpdrive.github.io/Apps/testApp.html
1st 3DMouse will control via 5DOF, 2nd 3DMouse will control 6DOF. (In 5DOF mode roll will control zoom, something not possible in Google Earth.)
With GamePad API you can use multiple 3DMice at the same time, a 3DMice in each hand for 12 simultaneous axis. I made a webapp similar to this back in 2011 with Google Earth Plugin using JavaScript Joystick plugin, but Google has abandoned GE plugin service.
One can fly around the Earth in 6DOF using all axis of the 3DMouse
https://www.youtube.com/watch?v=OX9yzfC ... MDtsro6ENh