fix image rendering on firefox

includes/style.css

@@ -18,6 +18,7 @@ a {
   color: #f69f8f;
 }
 canvas {
+  image-rendering: -moz-crisp-edges;
   image-rendering: pixelated;
 }
 input[type="color"] {

includes/style.less

@@ -26,6 +26,7 @@ a {
 }
 
 canvas {
+    image-rendering: -moz-crisp-edges;
     image-rendering: pixelated;
 }