--- a/layout/style/nsCSSKeywordList.h
+++ b/layout/style/nsCSSKeywordList.h
@@ -79,18 +79,20 @@ CSS_KEY(-moz-image-rect, _moz_image_rect
 CSS_KEY(-moz-info, _moz_info)
 CSS_KEY(-moz-inline-box, _moz_inline_box)
 CSS_KEY(-moz-inline-grid, _moz_inline_grid)
 CSS_KEY(-moz-inline-stack, _moz_inline_stack)
 CSS_KEY(-moz-isolate, _moz_isolate)
 CSS_KEY(-moz-isolate-override, _moz_isolate_override)
 CSS_KEY(-moz-left, _moz_left)
 CSS_KEY(-moz-list, _moz_list)
+CSS_KEY(-moz-mac-buttonactivetext, _moz_mac_buttonactivetext)
 CSS_KEY(-moz-mac-chrome-active, _moz_mac_chrome_active)
 CSS_KEY(-moz-mac-chrome-inactive, _moz_mac_chrome_inactive)
+CSS_KEY(-moz-mac-defaultbuttontext, _moz_mac_defaultbuttontext)
 CSS_KEY(-moz-mac-focusring, _moz_mac_focusring)
 CSS_KEY(-moz-mac-fullscreen-button, _moz_mac_fullscreen_button)
 CSS_KEY(-moz-mac-menuselect, _moz_mac_menuselect)
 CSS_KEY(-moz-mac-menushadow, _moz_mac_menushadow)
 CSS_KEY(-moz-mac-menutextdisable, _moz_mac_menutextdisable)
 CSS_KEY(-moz-mac-menutextselect, _moz_mac_menutextselect)
 CSS_KEY(-moz-mac-disabledtoolbartext, _moz_mac_disabledtoolbartext)
 CSS_KEY(-moz-mac-secondaryhighlight, _moz_mac_secondaryhighlight)

--- a/layout/style/nsCSSProps.cpp
+++ b/layout/style/nsCSSProps.cpp
@@ -943,18 +943,20 @@ const KTableValue nsCSSProps::kColorKTab
   eCSSKeyword__moz_default_background_color, NS_COLOR_MOZ_DEFAULT_BACKGROUND_COLOR,
   eCSSKeyword__moz_default_color, NS_COLOR_MOZ_DEFAULT_COLOR,
   eCSSKeyword__moz_dialog, LookAndFeel::eColorID__moz_dialog,
   eCSSKeyword__moz_dialogtext, LookAndFeel::eColorID__moz_dialogtext,
   eCSSKeyword__moz_dragtargetzone, LookAndFeel::eColorID__moz_dragtargetzone,
   eCSSKeyword__moz_hyperlinktext, NS_COLOR_MOZ_HYPERLINKTEXT,
   eCSSKeyword__moz_html_cellhighlight, LookAndFeel::eColorID__moz_html_cellhighlight,
   eCSSKeyword__moz_html_cellhighlighttext, LookAndFeel::eColorID__moz_html_cellhighlighttext,
+  eCSSKeyword__moz_mac_buttonactivetext, LookAndFeel::eColorID__moz_mac_buttonactivetext,
   eCSSKeyword__moz_mac_chrome_active, LookAndFeel::eColorID__moz_mac_chrome_active,
   eCSSKeyword__moz_mac_chrome_inactive, LookAndFeel::eColorID__moz_mac_chrome_inactive,
+  eCSSKeyword__moz_mac_defaultbuttontext, LookAndFeel::eColorID__moz_mac_defaultbuttontext,
   eCSSKeyword__moz_mac_focusring, LookAndFeel::eColorID__moz_mac_focusring,
   eCSSKeyword__moz_mac_menuselect, LookAndFeel::eColorID__moz_mac_menuselect,
   eCSSKeyword__moz_mac_menushadow, LookAndFeel::eColorID__moz_mac_menushadow,
   eCSSKeyword__moz_mac_menutextdisable, LookAndFeel::eColorID__moz_mac_menutextdisable,
   eCSSKeyword__moz_mac_menutextselect, LookAndFeel::eColorID__moz_mac_menutextselect,
   eCSSKeyword__moz_mac_disabledtoolbartext, LookAndFeel::eColorID__moz_mac_disabledtoolbartext,
   eCSSKeyword__moz_mac_secondaryhighlight, LookAndFeel::eColorID__moz_mac_secondaryhighlight,
   eCSSKeyword__moz_menuhover, LookAndFeel::eColorID__moz_menuhover,

--- a/toolkit/themes/osx/global/button.css
+++ b/toolkit/themes/osx/global/button.css
@@ -9,16 +9,32 @@ button {
   /* The horizontal margin used here come from the Aqua Human Interface
      Guidelines, there should be 12 pixels between two buttons. */
   margin: 5px 6px 3px;
   min-width: 79px;
   color: ButtonText;
   text-shadow: none;
 }
 
+button:hover:active {
+  color: -moz-mac-buttonactivetext;
+}
+
+/* When the window isn't focused, the default button background isn't drawn,
+ * so don't change the text color then: */
+button[default="true"]:not(:-moz-window-inactive) {
+  color: -moz-mac-defaultbuttontext;
+}
+
+/* Likewise, when active (mousedown) but not hovering, the default button
+ * background isn't drawn, override the previous selector for that case: */
+button[default="true"]:not(:hover):active {
+  color: ButtonText;
+}
+
 .button-text {
   margin: 1px 0 !important;
   -moz-margin-start: 3px !important;
   -moz-margin-end: 2px !important;
   text-align: center;
 }
 
 .button-icon {

--- a/widget/LookAndFeel.h
+++ b/widget/LookAndFeel.h
@@ -121,20 +121,24 @@ public:
     eColorID__moz_menubarhovertext,
     // On platforms where these colors are the same as
     // -moz-field, use -moz-fieldtext as foreground color
     eColorID__moz_eventreerow,
     eColorID__moz_oddtreerow,
 
     // colors needed by the Mac OS X theme
 
+    // foreground color of :hover:active buttons
+    eColorID__moz_mac_buttonactivetext,
     // background color of chrome toolbars in active windows
     eColorID__moz_mac_chrome_active,
     // background color of chrome toolbars in inactive windows
     eColorID__moz_mac_chrome_inactive,
+    // foreground color of default buttons
+    eColorID__moz_mac_defaultbuttontext,
     //ring around text fields and lists
     eColorID__moz_mac_focusring,
     //colour used when mouse is over a menu item
     eColorID__moz_mac_menuselect,
     //colour used to do shadows on menu items
     eColorID__moz_mac_menushadow,
     // color used to display text for disabled menu items
     eColorID__moz_mac_menutextdisable,

--- a/widget/cocoa/nsLookAndFeel.mm
+++ b/widget/cocoa/nsLookAndFeel.mm
@@ -132,16 +132,23 @@ nsLookAndFeel::NativeGetColor(ColorID aI
       // It's really hard to effectively map these to the Appearance Manager properly,
       // since they are modeled word for word after the win32 system colors and don't have any 
       // real counterparts in the Mac world. I'm sure we'll be tweaking these for 
       // years to come. 
       //
       // Thanks to mpt26@student.canterbury.ac.nz for the hardcoded values that form the defaults
       //  if querying the Appearance Manager fails ;)
       //
+    case eColorID__moz_mac_buttonactivetext:
+    case eColorID__moz_mac_defaultbuttontext:
+      if (nsCocoaFeatures::OnYosemiteOrLater()) {
+        aColor = NS_RGB(0xFF,0xFF,0xFF);
+        break;
+      }
+      // Otherwise fall through and return the regular button text:
       
     case eColorID_buttontext:
     case eColorID__moz_buttonhovertext:
       aColor = GetColorFromNSColor([NSColor controlTextColor]);
       break;
     case eColorID_captiontext:
     case eColorID_menutext:
     case eColorID_infotext:

--- a/widget/tests/test_platform_colors.xul
+++ b/widget/tests/test_platform_colors.xul
@@ -61,18 +61,20 @@ var colors = {
   "-moz-field": ["rgb(255, 255, 255)"],
   "-moz-fieldtext": ["rgb(0, 0, 0)"],
   "-moz-dialog": ["rgb(232, 232, 232)"],
   "-moz-dialogtext": ["rgb(0, 0, 0)"],
   "-moz-dragtargetzone": ["rgb(199, 208, 218)", "rgb(198, 198, 198)", "rgb(180, 213, 255)", "rgb(250, 236, 115)", "rgb(255, 176, 139)", "rgb(255, 209, 129)", "rgb(194, 249, 144)", "rgb(232, 184, 255)"],
   "-moz-hyperlinktext": ["rgb(0, 0, 238)"],
   "-moz-html-cellhighlight": ["rgb(212, 212, 212)"],
   "-moz-html-cellhighlighttext": ["rgb(0, 0, 0)"],
+  "-moz-mac-buttonactivetext": ["rgb(0, 0, 0)", "rgb(255, 255, 255)"],
   "-moz-mac-chrome-active": ["rgb(150, 150, 150)", "rgb(167, 167, 167)", "rgb(178, 178, 178)"],
   "-moz-mac-chrome-inactive": ["rgb(202, 202, 202)", "rgb(216, 216, 216)", "rgb(225, 225, 225)"],
+  "-moz-mac-defaultbuttontext": ["rgb(0, 0, 0)", "rgb(255, 255, 255)"],
   //"-moz-mac-focusring": ["rgb(83, 144, 210)", "rgb(95, 112, 130)", "rgb(63, 152, 221)", "rgb(108, 126, 141)"],
   "-moz-mac-menuselect": ["rgb(115, 132, 153)", "rgb(127, 127, 127)", "rgb(56, 117, 215)", "rgb(255, 193, 31)", "rgb(243, 70, 72)", "rgb(255, 138, 34)", "rgb(102, 197, 71)", "rgb(140, 78, 184)"],
   "-moz-mac-menushadow": ["rgb(163, 163, 163)"],
   "-moz-mac-menutextdisable": ["rgb(152, 152, 152)"],
   "-moz-mac-menutextselect": ["rgb(255, 255, 255)"],
   "-moz-mac-disabledtoolbartext": ["rgb(127, 127, 127)"],
   "-moz-mac-secondaryhighlight": ["rgb(212, 212, 212)"],
   "-moz-menuhover": ["rgb(115, 132, 153)", "rgb(127, 127, 127)", "rgb(56, 117, 215)", "rgb(255, 193, 31)", "rgb(243, 70, 72)", "rgb(255, 138, 34)", "rgb(102, 197, 71)", "rgb(140, 78, 184)"],

--- a/widget/xpwidgets/nsXPLookAndFeel.cpp
+++ b/widget/xpwidgets/nsXPLookAndFeel.cpp
@@ -210,18 +210,20 @@ const char nsXPLookAndFeel::sColorPrefs[
   "ui.-moz-buttonhoverface",
   "ui.-moz_buttonhovertext",
   "ui.-moz_menuhover",
   "ui.-moz_menuhovertext",
   "ui.-moz_menubartext",
   "ui.-moz_menubarhovertext",
   "ui.-moz_eventreerow",
   "ui.-moz_oddtreerow",
+  "ui.-moz-mac-buttonactivetext",
   "ui.-moz_mac_chrome_active",
   "ui.-moz_mac_chrome_inactive",
+  "ui.-moz-mac-defaultbuttontext",
   "ui.-moz-mac-focusring",
   "ui.-moz-mac-menuselect",
   "ui.-moz-mac-menushadow",
   "ui.-moz-mac-menutextdisable",
   "ui.-moz-mac-menutextselect",
   "ui.-moz_mac_disabledtoolbartext",
   "ui.-moz-mac-secondaryhighlight",
   "ui.-moz-win-mediatext",