--- a/toolkit/themes/linux/global/tree.css
+++ b/toolkit/themes/linux/global/tree.css
@@ -257,27 +257,16 @@ treechildren::-moz-tree-twisty(open) {
   width: 9px; /* The image's width is 9 pixels */
   list-style-image: url("chrome://global/skin/tree/twisty-open.png");
 }
 
 treechildren::-moz-tree-indentation {
   width: 18px;
 }
 
-/* ::::: gridline style ::::: */
-
-treechildren.gridlines::-moz-tree-cell {
-  border-right: 1px solid transparent !important;
-  border-bottom: 1px solid transparent !important;
-}
-
-treechildren.gridlines::-moz-tree-row {
-  border: none;
-}
-
 /* ::::: editable tree ::::: */
 
 treechildren::-moz-tree-row(selected, editing) {
   background-color: transparent;
   border: none;
 }
 
 treechildren::-moz-tree-cell-text(selected, editing) {

--- a/toolkit/themes/osx/global/tree.css
+++ b/toolkit/themes/osx/global/tree.css
@@ -217,27 +217,16 @@ treechildren::-moz-tree-twisty(open) {
 treechildren::-moz-tree-twisty(Name, separator) {
   -moz-appearance: none;
 }
 
 treechildren::-moz-tree-indentation {
   width: 16px;
 }
 
-/* ::::: gridline style ::::: */
-
-treechildren.gridlines::-moz-tree-cell {
-  border-inline-end: 1px solid GrayText;
-  border-bottom: 1px solid GrayText;
-}
-
-treechildren.gridlines::-moz-tree-row {
-  border: none;
-}
-
 /* ::::: editable tree ::::: */
 
 .tree-input {
   -moz-appearance: none;
   border-width: 0;
   box-shadow: var(--focus-ring-box-shadow);
   margin: 0;
   margin-inline-start: -2px;

--- a/toolkit/themes/windows/global/tree.css
+++ b/toolkit/themes/windows/global/tree.css
@@ -310,27 +310,16 @@ treechildren:-moz-locale-dir(rtl)::-moz-
 treechildren:-moz-locale-dir(rtl)::-moz-tree-twisty(hover, open) {
   list-style-image: url("chrome://global/skin/tree/twisty.svg#open-hover-rtl");
 }
 
 treechildren::-moz-tree-indentation {
   width: 12px;
 }
 
-/* ::::: gridline style ::::: */
-
-treechildren.gridlines::-moz-tree-cell {
-  border-right: 1px solid transparent !important;
-  border-bottom: 1px solid transparent !important;
-}
-
-treechildren.gridlines::-moz-tree-row {
-  border: none;
-}
-
 /* ::::: editable tree ::::: */
 
 treechildren::-moz-tree-row(selected, editing) {
   background-color: transparent;
   border: none;
 }
 
 treechildren::-moz-tree-cell-text(selected, editing) {