--- a/toolkit/themes/linux/global/button.css
+++ b/toolkit/themes/linux/global/button.css
@@ -9,22 +9,16 @@
 @namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul");
 
 /* :::::::::: button :::::::::: */
 
 button {
   -moz-appearance: button;
   margin: 1px 5px 2px 5px;
   min-width: 6.3em;
-  border: 3px solid;
-  -moz-border-top-colors: transparent ThreeDHighlight ThreeDLightShadow;
-  -moz-border-right-colors: transparent ThreeDDarkShadow ThreeDShadow;
-  -moz-border-bottom-colors: transparent ThreeDDarkShadow ThreeDShadow;
-  -moz-border-left-colors: transparent ThreeDHighlight ThreeDLightShadow;
-  background-color: ThreeDFace;
   color: ButtonText;
   text-shadow: none;
 }
 
 .button-box {
   -moz-appearance: button-focus;
   border: 1px solid transparent;
   padding-top: 1px;
@@ -39,72 +33,47 @@ button {
 
 .button-text {
   margin: 0 !important;
   text-align: center;
 }
 
 /* .......... focused state .......... */
 
-button:focus {
-  -moz-border-top-colors: ThreeDDarkShadow ThreeDHighlight transparent;
-  -moz-border-right-colors: ThreeDDarkShadow ThreeDDarkShadow ThreeDShadow;
-  -moz-border-bottom-colors: ThreeDDarkShadow ThreeDDarkShadow ThreeDShadow;
-  -moz-border-left-colors: ThreeDDarkShadow ThreeDHighlight transparent;
-}
-
 button:focus > .button-box {
   border: 1px dotted ThreeDDarkShadow;
 }
 
-/* .......... default state .......... */
-
-button[default="true"] {
-  -moz-border-top-colors: ThreeDDarkShadow ThreeDHighlight ThreeDLightShadow;
-  -moz-border-right-colors: ThreeDDarkShadow ThreeDDarkShadow ThreeDShadow;
-  -moz-border-bottom-colors: ThreeDDarkShadow ThreeDDarkShadow ThreeDShadow;
-  -moz-border-left-colors: ThreeDDarkShadow ThreeDHighlight ThreeDLightShadow;
-}
-
 /* .......... hover state .......... */
 
 button:hover {
   color: -moz-buttonhovertext;
-  background-color: -moz-buttonhoverface;
 }
 
 /* .......... active/open/checked state .......... */
 
 button:hover:active,
 button[open="true"],
 button[checked="true"] {
-  -moz-border-top-colors: ThreeDDarkShadow ThreeDShadow transparent;
-  -moz-border-right-colors: ThreeDDarkShadow ThreeDShadow transparent;
-  -moz-border-bottom-colors: ThreeDDarkShadow ThreeDShadow transparent;
-  -moz-border-left-colors: ThreeDDarkShadow ThreeDShadow transparent;
   color: ButtonText;
 }
 
 button:hover:active > .button-box,
 button[open="true"] > .button-box,
 button[checked="true"] > .button-box {
   padding-top: 2px;
   padding-bottom: 1px;
   padding-inline-start: 4px;
   padding-inline-end: 3px;
 }
 
 /* .......... disabled state .......... */
 
 button[disabled="true"],
 button[disabled="true"]:hover:active {
-  -moz-border-top-colors: transparent ThreeDHighlight ThreeDLightShadow !important;
-  -moz-border-right-colors: transparent ThreeDDarkShadow ThreeDShadow !important;
-  -moz-border-bottom-colors: transparent ThreeDDarkShadow ThreeDShadow !important;
-  -moz-border-left-colors: transparent ThreeDHighlight ThreeDLightShadow !important;
   color: GrayText;
 }
 
 button[disabled="true"] > .button-box {
   padding-top: 1px !important;
   padding-bottom: 2px !important;
   padding-inline-start: 3px !important;
   padding-inline-end: 4px !important;
@@ -127,26 +96,22 @@ button[type="menu-button"] {
 
 .button-menubutton-dropmarker {
   margin-inline-end: 3px;
 }
 
 /* ::::: plain buttons ::::: */
 
 button.plain {
-  border: 0px !important;
-  margin: 0px !important;
-  padding: 0px !important;
+  margin: 0 !important;
+  padding: 0 !important;
 }
 
 button[type="disclosure"] {
-  border: 0px !important;
-  margin: 0px !important;
-  padding: 0px !important;
+  margin: 0;
   -moz-appearance: none;
   list-style-image: url("chrome://global/skin/tree/twisty-clsd.png");
-  min-width: 0px !important;
-  background-color: transparent;
+  min-width: 0;
 }
 
 button[type="disclosure"][open="true"] {
   list-style-image: url("chrome://global/skin/tree/twisty-open.png"); 
 }

--- a/toolkit/themes/shared/popupnotification.inc.css
+++ b/toolkit/themes/shared/popupnotification.inc.css
@@ -73,19 +73,16 @@
   outline: 1px solid var(--arrowpanel-dimmed-further);
   background-color: var(--arrowpanel-dimmed-further);
   box-shadow: 0 1px 0 hsla(210,4%,10%,.05) inset;
 }
 
 .popup-notification-button[disabled] {
   background-color: var(--arrowpanel-dimmed-further);
   color: graytext;
-  /* the !important is to override the button[disabled] settings in
-   * windows/linux button.css */
-  -moz-border-top-colors: var(--panel-separator-color) !important;
 }
 
 .popup-notification-button[default] {
   flex: 0 50%;
 }
 
 .popup-notification-button[default]:not([disabled]) {
   background-color: #0996f8;

--- a/toolkit/themes/windows/global/button.css
+++ b/toolkit/themes/windows/global/button.css
@@ -9,22 +9,16 @@
 @namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul");
 
 /* :::::::::: button :::::::::: */
 
 button {
   -moz-appearance: button;
   margin: 1px 5px 2px 5px;
   min-width: 6.3em;
-  border: 3px solid;
-  -moz-border-top-colors: transparent ThreeDHighlight ThreeDLightShadow;
-  -moz-border-right-colors: transparent ThreeDDarkShadow ThreeDShadow;
-  -moz-border-bottom-colors: transparent ThreeDDarkShadow ThreeDShadow;
-  -moz-border-left-colors: transparent ThreeDHighlight ThreeDLightShadow;
-  background-color: ThreeDFace;
   color: ButtonText;
   text-shadow: none;
 }
 
 .button-box {
   border: 1px solid transparent;
   padding-top: 1px;
   padding-bottom: 2px;
@@ -34,73 +28,46 @@ button {
 
 .button-text {
   margin: 0 !important;
   text-align: center;
 }
 
 /* .......... focused state .......... */
 
-button:focus {
-  -moz-border-top-colors: ThreeDDarkShadow ThreeDHighlight transparent;
-  -moz-border-right-colors: ThreeDDarkShadow ThreeDDarkShadow ThreeDShadow;
-  -moz-border-bottom-colors: ThreeDDarkShadow ThreeDDarkShadow ThreeDShadow;
-  -moz-border-left-colors: ThreeDDarkShadow ThreeDHighlight transparent;
-}
-
 button:-moz-focusring > .button-box {
   border: 1px dotted ThreeDDarkShadow;
 }
 
 /* .......... default state .......... */
 
-button[default="true"] {
-  -moz-border-top-colors: ThreeDDarkShadow ThreeDHighlight ThreeDLightShadow;
-  -moz-border-right-colors: ThreeDDarkShadow ThreeDDarkShadow ThreeDShadow;
-  -moz-border-bottom-colors: ThreeDDarkShadow ThreeDDarkShadow ThreeDShadow;
-  -moz-border-left-colors: ThreeDDarkShadow ThreeDHighlight ThreeDLightShadow;
-}
-
 @media (-moz-windows-default-theme: 0) {
   @media (-moz-windows-compositor) {
     /* This is for high-contrast themes on Windows 8 and later */
     button[default="true"],
     button:hover {
       color: HighlightText;
     }
   }
 }
 
 /* .......... active/open/checked state .......... */
 
-button:hover:active,
-button[open="true"],
-button[checked="true"] {
-  -moz-border-top-colors: ThreeDDarkShadow ThreeDShadow transparent;
-  -moz-border-right-colors: ThreeDDarkShadow ThreeDShadow transparent;
-  -moz-border-bottom-colors: ThreeDDarkShadow ThreeDShadow transparent;
-  -moz-border-left-colors: ThreeDDarkShadow ThreeDShadow transparent;
-}
-
 button:hover:active > .button-box:-moz-system-metric(windows-classic),
 button[open="true"] > .button-box:-moz-system-metric(windows-classic),
 button[checked="true"] > .button-box:-moz-system-metric(windows-classic) {
   padding-top: 2px;
   padding-bottom: 1px;
   padding-inline-start: 4px;
   padding-inline-end: 3px;
 }
 
 /* .......... disabled state .......... */
 
 button[disabled="true"] {
-  -moz-border-top-colors: transparent ThreeDHighlight ThreeDLightShadow !important;
-  -moz-border-right-colors: transparent ThreeDDarkShadow ThreeDShadow !important;
-  -moz-border-bottom-colors: transparent ThreeDDarkShadow ThreeDShadow !important;
-  -moz-border-left-colors: transparent ThreeDHighlight ThreeDLightShadow !important;
   color: GrayText;
 }
 
 button[disabled="true"]:-moz-system-metric(windows-classic) {
   color: ThreeDShadow;
   text-shadow: 1px 1px ThreeDHighlight;
 }
 
@@ -110,17 +77,16 @@ button[disabled="true"] > .button-box {
   padding-inline-start: 3px !important;
   padding-inline-end: 4px !important;
 }
 
 /* ::::: menu/menu-button buttons ::::: */
 
 button[type="menu-button"] {
   margin: 0;
-  border: none;
 }
 
 .button-menu-dropmarker,
 .button-menubutton-dropmarker {
   -moz-appearance: none !important;
   margin: 1px;
   background-color: transparent;
   border: none;
@@ -133,26 +99,22 @@ button[type="menu-button"] {
   margin-bottom: 0px;
   margin-inline-start: 2px;
   margin-inline-end: 0px;
 }
 
 /* ::::: plain buttons ::::: */
 
 button.plain {
-  border: 0px !important;
-  margin: 0px !important;
-  padding: 0px !important;
+  margin: 0 !important;
+  padding: 0 !important;
 }
 
 button[type="disclosure"] {
-  border: 0px !important;
-  margin: 0px !important;
-  padding: 0px !important;
+  margin: 0;
   -moz-appearance: none;
   list-style-image: url("chrome://global/skin/tree/twisty.svg#clsd");
-  min-width: 0px !important;
-  background-color: transparent;
+  min-width: 0;
 }
 
 button[type="disclosure"][open="true"] {
   list-style-image: url("chrome://global/skin/tree/twisty.svg#open");
 }