diff --git a/src/wp-admin/css/common.css b/src/wp-admin/css/common.css
index 36022990a8..32c10cbe2a 100644
--- a/src/wp-admin/css/common.css
+++ b/src/wp-admin/css/common.css
@@ -3150,7 +3150,6 @@ img {
 	font-family: Consolas, Monaco, monospace;
 	font-size: 13px;
 	background: #f6f7f7;
-	-moz-tab-size: 4;
 	-o-tab-size: 4;
 	tab-size: 4;
 }
diff --git a/src/wp-admin/css/customize-controls.css b/src/wp-admin/css/customize-controls.css
index c631b456aa..a7129bbafd 100644
--- a/src/wp-admin/css/customize-controls.css
+++ b/src/wp-admin/css/customize-controls.css
@@ -1605,7 +1605,6 @@ p.customize-section-description {
 	font-family: Consolas, Monaco, monospace;
 	font-size: 12px;
 	padding: 6px 8px;
-	-moz-tab-size: 2;
 	-o-tab-size: 2;
 	tab-size: 2;
 }