CSS gradient checkerboard pattern

I want to create a checkerboard pattern using gradients. I've found an example and modified it to my needs, however it only works with -moz prefix. When I remove the -moz prefix, the pattern is completely different.

How can I make this -moz checkerboard pattern work with unprefixed linear-gradient?

body {
  background-image:
  linear-gradient(45deg, #808080 25%, transparent 25%), 
  linear-gradient(-45deg, #808080 25%, transparent 25%),
  linear-gradient(45deg, transparent 75%, #808080 75%),
  linear-gradient(-45deg, transparent 75%, #808080 75%);

  background-size:20px 20px;    
  background-position:0 0, 10px 0, 10px -10px, 0px 10px;
}

Just modify the background-position like in the below snippet to get the required output. This works fine in Firefox, Chrome, Opera, IE11 and Edge.

body {
  background-image: linear-gradient(45deg, #808080 25%, transparent 25%), linear-gradient(-45deg, #808080 25%, transparent 25%), linear-gradient(45deg, transparent 75%, #808080 75%), linear-gradient(-45deg, transparent 75%, #808080 75%);
  background-size: 20px 20px;
  background-position: 0 0, 0 10px, 10px -10px, -10px 0px;
}

The problem seems to be happening because of a difference in the way the angles are handled by the -moz linear gradient and the standard one. -45deg in the -moz linear gradient seems to be equal to 135deg in the standard gradient (but changing the angle is resulting in a strange dot in the middle).

The below screenshots show the difference (both taken in the latest Firefox v44.0).

Output with -moz-linear-gradient:

Output with linear gradient: