devices.json is a catalog of common web-enabled devices and their properties.

{
  TYPES: [ "phones", … ],
  phones: [
    {
      name: "LePhone",
      width: 360,
      height: 640,
      pixelRatio: 3,
      userAgent: "Mozilla/5.0 (Mobile; rv:39.0) Gecko/39.0 Firefox/39.0",
      touch: true,
      firefoxOS: true
    }
  ], …
}

• name brand and model(s).
• width viewport width.
• height viewport height.
• pixelRatio ratio from viewport to physical screen pixels.
• userAgent UA string of the device's browser.
• touch whether it has a touch screen.
• firefoxOS whether Firefox OS is supported.
• os the OS type it usually ships with.

• phones (smart phones)
• tablets
• laptops
• televisions
• consoles (gaming consoles)
• watches (smart watches)

• Stable: Mozilla CDN.
• Latest: GitHub.

• Use the check.html helper.
• Use node test.js to verify your devices.json.
• Submit pull requests.

• Chrome Devtools: emulated_devices/module.json.
• Wikipedia: Comparison of Firefox OS devices.
• MDN: Firefox OS compatible devices.
• My Tesla Motors: Model S Web Browser Capabilities.
• Various other online sources.