Tsengar: Gamepad isn't supported in FF at the moment.
To have the test working in FF, you are supposed to install the old version 11 nightly with the beta support compiled in, which is kind of a burden.
For Chrome, as far as I know, you have to press buttons on the gamepad first to "enable" it and mostly only XBox360 gamepad is supported. (to be confirmed, Ashley ?)
Support for other gamepad is coming though and support in FF is being worked on too, but isn't yet included in any stable release.
There were some movements in the bugzilla about gamepad support, so hopefully it's coming for FF.