--- a/layout/style/test/property_database.js
+++ b/layout/style/test/property_database.js
@@ -6910,58 +6910,59 @@ function SupportsMaskShorthand() {
 
 if (SupportsMaskShorthand()) {
   gCSSProperties["mask"] = {
     domProp: "mask",
     inherited: false,
     type: CSS_TYPE_SHORTHAND_AND_LONGHAND,
     /* FIXME: All mask-border-* should be added when we implement them. */
     subproperties: ["mask-clip", "mask-image", "mask-mode", "mask-origin", "mask-position-x", "mask-position-y", "mask-repeat", "mask-size" , "mask-composite"],
-    initial_values: [ "match-source", "none", "no-repeat", "add", "0% 0%", "top left", "left top", "0% 0% / auto", "top left / auto", "left top / auto", "0% 0% / auto auto",
-      "top left none", "left top none", "none left top", "none top left", "none 0% 0%", "left top / auto none", "left top / auto auto none",
-      "match-source none no-repeat add top left", "left top no-repeat none add", "none no-repeat add top left / auto", "left top / auto no-repeat none add match-source", "none no-repeat add 0% 0% / auto auto match-source",
+    initial_values: [ "match-source", "none", "no-repeat", "add", "50% 50%", "center center", "50% 50% / auto", "center / auto", "center center / auto", "50% 50% / auto auto",
+      "center none", "center center none", "none center", "none center center", "none 50% 50%", "center / auto none",
+      "center center / auto auto none",
+      "match-source none no-repeat add center center", "center centerp no-repeat none add", "none no-repeat add center center / auto", "center center / auto no-repeat none add match-source", "none no-repeat add 0% 0% / auto auto match-source",
       "border-box", "border-box border-box" ],
     other_values: [
-      "none alpha no-repeat add left top",
+      "none alpha no-repeat add center",
       "url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAACAAAAAgCAIAAAD8GO2jAAAAKElEQVR42u3NQQ0AAAgEoNP+nTWFDzcoQE1udQQCgUAgEAgEAsGTYAGjxAE/G/Q2tQAAAABJRU5ErkJggg==)",
-      "no-repeat url('data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAACAAAAAgCAIAAAD8GO2jAAAAKElEQVR42u3NQQ0AAAgEoNP+nTWFDzcoQE1udQQCgUAgEAgEAsGTYAGjxAE/G/Q2tQAAAABJRU5ErkJggg==') alpha left top add",
+      "no-repeat url('data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAACAAAAAgCAIAAAD8GO2jAAAAKElEQVR42u3NQQ0AAAgEoNP+nTWFDzcoQE1udQQCgUAgEAgEAsGTYAGjxAE/G/Q2tQAAAABJRU5ErkJggg==') alpha center add",
       "repeat-x",
       "repeat-y",
       "repeat",
-      "none repeat-y alpha add 0% 0%",
+      "none repeat-y alpha add 50% 50%",
       "subtract",
-      "0% top subtract alpha no-repeat none",
+      "50% center subtract alpha no-repeat none",
       "top",
       "left",
-      "50% 50%",
-      "center",
-      "top / 100px",
-      "left / contain",
-      "left / cover",
+      "0% 0%",
+      "top left",
+      "center / 100px",
+      "center / contain",
+      "center / cover",
       "10px / 10%",
       "10em / calc(20px)",
-      "top left / 100px 100px",
-      "top left / 100px auto",
-      "top left / 100px 10%",
-      "top left / 100px calc(20px)",
+      "center center / 100px 100px",
+      "center center / 100px auto",
+      "center center / 100px 10%",
+      "center center / 100px calc(20px)",
       "bottom right add none alpha no-repeat",
-      "50% alpha",
-      "alpha 50%",
-      "50%",
+      "0% alpha",
+      "alpha 0%",
+      "0%",
       "url(#mymask)",
       "-moz-radial-gradient(10% bottom, #ffffff, black) add repeat",
       "-moz-linear-gradient(10px 10px -45deg, red, blue) no-repeat",
       "-moz-linear-gradient(10px 10px -0.125turn, red, blue) no-repeat",
       "-moz-repeating-radial-gradient(10% bottom, #ffffff, black) add repeat",
       "-moz-repeating-linear-gradient(10px 10px -45deg, red, blue) no-repeat",
       "-moz-element(#test) alpha",
       /* multiple mask-image */
       "url(404.png), url(404.png)",
       "repeat-x, subtract, none",
-      "0% top url(404.png), url(404.png) 0% top",
+      "50% top url(404.png), url(404.png) 50% top",
       "subtract repeat-y top left url(404.png), repeat-x alpha",
       "url(404.png), -moz-linear-gradient(20px 20px -45deg, blue, green), -moz-element(#a) alpha",
       "top left / contain, bottom right / cover",
       /* test cases with clip+origin in the shorthand */
       "url(404.png) alpha padding-box",
       "url(404.png) border-box alpha",
       "content-box url(404.png)",
       "url(404.png) alpha padding-box padding-box",
@@ -7035,18 +7036,19 @@ if (SupportsMaskShorthand()) {
     initial_values: [ "border-box" ],
     other_values: [ "padding-box", "content-box", "border-box, padding-box", "padding-box, padding-box, padding-box", "border-box, border-box" ],
     invalid_values: [ "margin-box", "padding-box padding-box" ]
   };
   gCSSProperties["mask-position"] = {
     domProp: "maskPosition",
     inherited: false,
     type: CSS_TYPE_SHORTHAND_AND_LONGHAND,
-    initial_values: [ "top 0% left 0%", "top 0% left", "top left", "left top", "0% 0%", "0% top", "left 0%" ],
-    other_values: [ "top", "left", "right", "bottom", "center", "center bottom", "bottom center", "center right", "right center", "center top", "top center", "center left", "left center", "right bottom", "bottom right", "50%", "top left, top left", "top left, top right", "top right, top left", "left top, 0% 0%", "10% 20%, 30%, 40%", "top left, bottom right", "right bottom, left top", "0%", "0px", "30px", "0%, 10%, 20%, 30%", "top, top, top, top, top",
+    initial_values: [ "left 50% top 50%", "left 50% center", "center", "center center", "50% 50%", "50% center", "center 50%" ],
+    other_values: [ "top", "left", "right", "bottom", "center bottom", "bottom center", "center right", "right center", "center top", "top center", "center left", "left center", "right bottom", "bottom right", "0%", "top left, top left", "top left, top right", "top right, top left", "left top, 0% 0%", "10% 20%, 30%, 40%", "top left, bottom right", "right bottom, left top", "0%", "0px", "30px", "0%, 10%, 20%, 30%", "top, top, top, top, top",
+      "top 0% left 0%", "top 0% left", "top left", "left top", "0% 0%", "0% top", "left 0%",
       "calc(20px)",
       "calc(20px) 10px",
       "10px calc(20px)",
       "calc(20px) 25%",
       "25% calc(20px)",
       "calc(20px) calc(20px)",
       "calc(20px + 1em) calc(20px / 2)",
       "calc(20px + 50%) calc(50% - 10px)",