diff --git a/toolkit/components/aboutperformance/content/aboutPerformance.css b/toolkit/components/aboutperformance/content/aboutPerformance.css
index 33a42b859e3d..42275f1da02e 100644
--- a/toolkit/components/aboutperformance/content/aboutPerformance.css
+++ b/toolkit/components/aboutperformance/content/aboutPerformance.css
@@ -59,7 +59,7 @@ td:nth-child(5) {
 }
 
 /* Show action icons on selected or hovered rows */
-tr:-moz-any([selected], :hover) > td > .action-icon {
+tr:is([selected], :hover) > td > .action-icon {
   padding: 1px 10px;
   opacity: 1;
 }
diff --git a/toolkit/themes/linux/global/button.css b/toolkit/themes/linux/global/button.css
index 7a1c7c3fa986..88d178b01af5 100644
--- a/toolkit/themes/linux/global/button.css
+++ b/toolkit/themes/linux/global/button.css
@@ -30,13 +30,13 @@ button {
 
 /* .......... hover state .......... */
 
-button:hover:not(:-moz-any(:active,[disabled="true"],[open="true"],[checked="true"],[default="true"])) {
+button:hover:not(:is(:active,[disabled="true"],[open="true"],[checked="true"],[default="true"])) {
   color: -moz-buttonhovertext;
 }
 
 /* .......... active state .......... */
 
-button:-moz-any(:hover:active,[open="true"]):not([default="true"]):not([disabled="true"]) {
+button:is(:hover:active,[open="true"]):not([default="true"]):not([disabled="true"]) {
   color: -moz-gtk-buttonactivetext;
 }
 
diff --git a/toolkit/themes/linux/global/popup.css b/toolkit/themes/linux/global/popup.css
index bdca522023b3..2994dbebc892 100644
--- a/toolkit/themes/linux/global/popup.css
+++ b/toolkit/themes/linux/global/popup.css
@@ -54,40 +54,40 @@ panel[type="arrow"].panel-no-padding::part(arrowcontent) {
   overflow: hidden; /* Don't let panel content overflow the border */
 }
 
-:-moz-any(panel, menupopup)::part(arrow) {
+:is(panel, menupopup)::part(arrow) {
   -moz-context-properties: fill, stroke;
   fill: var(--arrowpanel-background);
   stroke: var(--arrowpanel-border-color);
 }
 
-:-moz-any(panel, menupopup)[side="top"]::part(arrow),
-:-moz-any(panel, menupopup)[side="bottom"]::part(arrow) {
+:is(panel, menupopup)[side="top"]::part(arrow),
+:is(panel, menupopup)[side="bottom"]::part(arrow) {
   list-style-image: url("chrome://global/skin/arrow/panelarrow-vertical.svg");
   position: relative;
   margin-inline: 10px;
 }
 
-:-moz-any(panel, menupopup)[side="top"]::part(arrow) {
+:is(panel, menupopup)[side="top"]::part(arrow) {
   margin-bottom: -5px;
 }
 
-:-moz-any(panel, menupopup)[side="bottom"]::part(arrow) {
+:is(panel, menupopup)[side="bottom"]::part(arrow) {
   transform: scaleY(-1);
   margin-top: -5px;
 }
 
-:-moz-any(panel, menupopup)[side="left"]::part(arrow),
-:-moz-any(panel, menupopup)[side="right"]::part(arrow) {
+:is(panel, menupopup)[side="left"]::part(arrow),
+:is(panel, menupopup)[side="right"]::part(arrow) {
   list-style-image: url("chrome://global/skin/arrow/panelarrow-horizontal.svg");
   position: relative;
   margin-block: 10px;
 }
 
-:-moz-any(panel, menupopup)[side="left"]::part(arrow) {
+:is(panel, menupopup)[side="left"]::part(arrow) {
   margin-right: -5px;
 }
 
-:-moz-any(panel, menupopup)[side="right"]::part(arrow) {
+:is(panel, menupopup)[side="right"]::part(arrow) {
   transform: scaleX(-1);
   margin-left: -5px;
 }
diff --git a/toolkit/themes/osx/global/popup.css b/toolkit/themes/osx/global/popup.css
index b601214f30c3..0888d8647b5d 100644
--- a/toolkit/themes/osx/global/popup.css
+++ b/toolkit/themes/osx/global/popup.css
@@ -67,32 +67,32 @@ panel[type="arrow"].panel-no-padding::part(arrowcontent) {
   overflow: hidden; /* Don't let panel content overflow the border-radius */
 }
 
-:-moz-any(panel, menupopup)::part(arrow) {
+:is(panel, menupopup)::part(arrow) {
   -moz-context-properties: fill, stroke;
   fill: var(--arrowpanel-background);
   stroke: var(--arrowpanel-border-color);
 }
 
-:-moz-any(panel, menupopup)[side="top"]::part(arrow) {
+:is(panel, menupopup)[side="top"]::part(arrow) {
   list-style-image: url("chrome://global/skin/arrow/panelarrow-vertical.svg");
   margin-inline: 16px;
   margin-bottom: -1px;
 }
 
-:-moz-any(panel, menupopup)[side="bottom"]::part(arrow) {
+:is(panel, menupopup)[side="bottom"]::part(arrow) {
   list-style-image: url("chrome://global/skin/arrow/panelarrow-vertical.svg");
   -moz-transform: scaleY(-1);
   margin-inline: 16px;
   margin-top: -1px;
 }
 
-:-moz-any(panel, menupopup)[side="left"]::part(arrow) {
+:is(panel, menupopup)[side="left"]::part(arrow) {
   list-style-image: url("chrome://global/skin/arrow/panelarrow-horizontal.svg");
   margin-block: 16px;
   margin-right: -1px;
 }
 
-:-moz-any(panel, menupopup)[side="right"]::part(arrow) {
+:is(panel, menupopup)[side="right"]::part(arrow) {
   list-style-image: url("chrome://global/skin/arrow/panelarrow-horizontal.svg");
   transform: scaleX(-1);
   margin-block: 16px;
diff --git a/toolkit/themes/windows/global/button.css b/toolkit/themes/windows/global/button.css
index c61f21fab51c..a8cb7bd9b330 100644
--- a/toolkit/themes/windows/global/button.css
+++ b/toolkit/themes/windows/global/button.css
@@ -44,7 +44,7 @@ button:-moz-focusring {
        default, hovered or focused state. However, if these states overlap with
        the active, disabled, open or checked state, the appearance reverts back
        to the default background. */
-    button:-moz-any([default="true"],:hover,:focus):not(:-moz-any(:active,[disabled="true"],[open="true"],[checked="true"])) {
+    button:is([default="true"],:hover,:focus):not(:is(:active,[disabled="true"],[open="true"],[checked="true"])) {
       color: HighlightText;
     }
   }
diff --git a/toolkit/themes/windows/global/menu.css b/toolkit/themes/windows/global/menu.css
index fcd4f3d5f5b3..8ad872e01a79 100644
--- a/toolkit/themes/windows/global/menu.css
+++ b/toolkit/themes/windows/global/menu.css
@@ -221,7 +221,7 @@ menulist > menupopup > menuitem[_moz-menuactive="true"][disabled="true"] {
   }
 }
 
-menulist > menupopup > :-moz-any(menuitem, menucaption):not(.menuitem-iconic) > .menu-iconic-text {
+menulist > menupopup > :is(menuitem, menucaption):not(.menuitem-iconic) > .menu-iconic-text {
   margin: 0 !important;
 }
 
diff --git a/toolkit/themes/windows/global/popup.css b/toolkit/themes/windows/global/popup.css
index 34a68d3ed171..71751df592ff 100644
--- a/toolkit/themes/windows/global/popup.css
+++ b/toolkit/themes/windows/global/popup.css
@@ -77,40 +77,40 @@ panel[type="arrow"].panel-no-padding::part(arrowcontent) {
   overflow: hidden; /* Don't let panel content overflow the border-radius */
 }
 
-:-moz-any(panel, menupopup)::part(arrow) {
+:is(panel, menupopup)::part(arrow) {
   -moz-context-properties: fill, stroke;
   fill: var(--arrowpanel-background);
   stroke: var(--arrowpanel-border-color);
 }
 
-:-moz-any(panel, menupopup)[side="top"]::part(arrow),
-:-moz-any(panel, menupopup)[side="bottom"]::part(arrow) {
+:is(panel, menupopup)[side="top"]::part(arrow),
+:is(panel, menupopup)[side="bottom"]::part(arrow) {
   list-style-image: url("chrome://global/skin/arrow/panelarrow-vertical.svg");
   position: relative;
   margin-inline: 10px;
 }
 
-:-moz-any(panel, menupopup)[side="top"]::part(arrow) {
+:is(panel, menupopup)[side="top"]::part(arrow) {
   margin-bottom: -5px;
 }
 
-:-moz-any(panel, menupopup)[side="bottom"]::part(arrow) {
+:is(panel, menupopup)[side="bottom"]::part(arrow) {
   transform: scaleY(-1);
   margin-top: -5px;
 }
 
-:-moz-any(panel, menupopup)[side="left"]::part(arrow),
-:-moz-any(panel, menupopup)[side="right"]::part(arrow) {
+:is(panel, menupopup)[side="left"]::part(arrow),
+:is(panel, menupopup)[side="right"]::part(arrow) {
   list-style-image: url("chrome://global/skin/arrow/panelarrow-horizontal.svg");
   position: relative;
   margin-block: 10px;
 }
 
-:-moz-any(panel, menupopup)[side="left"]::part(arrow) {
+:is(panel, menupopup)[side="left"]::part(arrow) {
   margin-right: -5px;
 }
 
-:-moz-any(panel, menupopup)[side="right"]::part(arrow) {
+:is(panel, menupopup)[side="right"]::part(arrow) {
   transform: scaleX(-1);
   margin-left: -5px;
 }