How to get an Xbox controller working in HTML5?

I know this is an old thread and it’s been deemed answered, but I have been working in 4.9, and via Launch I haven’t been able to get my game to pop up in Chrome or 64-bit Firefox, but in 32-bit Firefox I was able to get it up without a gamepad plugged in. When my gamepad is plugged in I receive an error in the image below.

After I select OK, I receive the text:
FSlateApplication::OnControllerButtonReleased?5()
undefined?T()
FHTML5InputInterface::SendControllerEvents()
FHTML5Application::PollGameDeviceState(float)
FSlateApplication::PollGameDeviceState()
FEngineLoop::Tick()
HTML5_Tick()
dynCall_v

I’m about to test this in 4.10, but I thought I’d add this for some info since the OP did not and it’s been a while and I’m getting an error.

Edit: It does appear to have the exact same problem in 4.10 with the error in the same file on a different line.