Reported in https://twitter.com/MoOx/status/790496791187914753 STR: - use nightly - open RDM on any page - choose the device "Laptop (1920 x 1080)" ==> The width/height fields at the bottom of RDM actually say that the viewport is 1280 x 720. This looks like a typo in the source device DB: https://code.cdn.mozilla.net/devices/devices.json

Thanks for filing! It's actually a bit more complex than it seems... 1280 x 720 is the CSS size, but the dPR is 1.5, so the "physical size" being emulated is 1920 x 1080. We're discussing how to handle this over in bug 1309292.