The triggers are actually axes. Left trigger is axis 9 and right trigger axis 10 just like the windows controller mapping here: http://wiki.unity3d.com/index.php?title=Xbox360Controller
However the buttons are not mapped consistently. From testing i found them to be mapped as such:
LTweb and RTweb are simply axes i added to my input manager that use the controller's axis 9 and 10.
switch (button){
case "RB":
return Input.GetKey("joystick button 5");

case "LB":
return Input.GetKey("joystick button 4");

case "RT":
return Input.GetAxis("RTweb") > 0;

case "LT":
return Input.GetAxis("LTweb") > 0;

case "DpadLeft":
return Input.GetKeyDown("joystick button 14");

case "DpadTop":
return Input.GetKeyDown("joystick button 12");

case "DpadRight":
return Input.GetKeyDown("joystick button 15");

case "DpadBottom":
return Input.GetKeyDown("joystick button 13");

case "back":
return Input.GetKeyDown("joystick button 6");

case "middle":
return Input.GetKeyDown("joystick button 16");

case "start":
return Input.GetKeyDown("joystick button 7");

case "X":
return Input.GetKeyDown("joystick button 2");

case "Y":
return Input.GetKeyDown("joystick button 3");

case "A":
return Input.GetKeyDown("joystick button 0");

case "B":
return Input.GetKeyDown("joystick button 1");

case "LeftStick":
return Input.GetKeyDown("joystick button 8");

case "RightStick":
return Input.GetKeyDown("joystick button 9");

Replicated also with a Xbox 360 controller on both of them: latest version of Google Chrome and Mozilla Firefox. Unity version 2017.3.1f1 (64-bit). Windows 7 x64 OS.

Issue still replicated using an XBox 360 controller
Tested with Firefox 57.0.4 (64-bit) and Unity Version 2017.3.0f3

Replicated this issue using an Xbox 360 controller.
Unity Version 2017.2.0f3
Tested on Firefox 57.0.2 (64-bit)