--- a/dom/animation/test/mozilla/file_discrete-animations.html
+++ b/dom/animation/test/mozilla/file_discrete-animations.html
@@ -70,21 +70,16 @@ const gMozillaSpecificProperties = {
     from: "-moz-crisp-edges",
     to: "auto"
   },
   "-moz-stack-sizing": {
     // https://developer.mozilla.org/en/docs/Web/CSS/-moz-stack-sizing
     from: "ignore",
     to: "stretch-to-fit"
   },
-  "-moz-tab-size": {
-    // https://drafts.csswg.org/css-text-3/#propdef-tab-size
-    from: "1",
-    to: "5"
-  },
   "-moz-text-size-adjust": {
     // https://drafts.csswg.org/css-size-adjust/#propdef-text-size-adjust
     from: "none",
     to: "auto"
   },
   "-webkit-text-stroke-width": {
     // https://compat.spec.whatwg.org/#propdef--webkit-text-stroke-width
     from: "10px",

--- a/layout/style/nsCSSPropList.h
+++ b/layout/style/nsCSSPropList.h
@@ -3873,17 +3873,17 @@ CSS_PROP_TEXT(
     _moz_tab_size,
     CSS_PROP_DOMPROP_PREFIXED(TabSize),
     CSS_PROPERTY_PARSE_VALUE |
         CSS_PROPERTY_VALUE_NONNEGATIVE,
     "",
     VARIANT_INHERIT | VARIANT_LNCALC,
     nullptr,
     offsetof(nsStyleText, mTabSize),
-    eStyleAnimType_Discrete)
+    eStyleAnimType_Coord)
 CSS_PROP_TABLE(
     table-layout,
     table_layout,
     TableLayout,
     CSS_PROPERTY_PARSE_VALUE,
     "",
     VARIANT_HK,
     kTableLayoutKTable,

--- a/layout/style/test/test_transitions_per_property.html
+++ b/layout/style/test/test_transitions_per_property.html
@@ -243,16 +243,18 @@ var supported_properties = {
     "stroke-opacity" : [ test_float_zeroToOne_transition,
                          // opacity is clamped in computed style
                          // (not parsing/interpolation)
                          test_float_zeroToOne_clamped ],
     // NOTE: when calc() is supported on 'stroke-width', we should add
     // test_length_percent_calc_transition.
     "stroke-width": [ test_length_transition_svg, test_percent_transition,
                       test_length_clamped_svg, test_percent_clamped ],
+    "-moz-tab-size": [ test_float_zeroToOne_transition,
+                       test_float_aboveOne_transition, test_length_clamped ],
     "text-decoration": [ test_color_shorthand_transition,
                          test_true_currentcolor_shorthand_transition ],
     "text-decoration-color": [ test_color_transition,
                                test_true_currentcolor_transition ],
     "text-emphasis-color": [ test_color_transition,
                              test_true_currentcolor_transition ],
     "text-indent": [ test_length_transition, test_percent_transition,
                      test_length_unclamped, test_percent_unclamped ],