diff --git a/core/modules/ckeditor5/css/essentials.admin.css b/core/modules/ckeditor5/css/essentials.admin.css
index 62a5ac434b9d3a019d288f078e79ef842662f0f3..429166121edd5200982b0d748933715ec78d0a80 100644
--- a/core/modules/ckeditor5/css/essentials.admin.css
+++ b/core/modules/ckeditor5/css/essentials.admin.css
@@ -1,6 +1,7 @@
 .ckeditor5-toolbar-button-divider {
   background-image: url(../icons/divider.svg);
 }
+
 .ckeditor5-toolbar-button-wrapping {
   background-image: url(../icons/separator.svg);
 }
@@ -20,15 +21,20 @@
   width: 100px;
   color: #000;
 }
+
 .ckeditor5-toolbar-button-heading::before {
   margin-left: 10px;
+  /* For browsers which don't support alt content, eg FireFox */
   content: "Heading";
+  content: "Heading" / "";
   font-size: 14px;
 }
+
 [dir="rtl"] .ckeditor5-toolbar-button-heading::before {
   margin-right: 10px;
   margin-left: 0;
 }
+
 .ckeditor5-toolbar-button-heading::after {
   display: inline-block;
   width: 7px;
@@ -39,6 +45,7 @@
   border-width: 2px 2px 0 0;
   border-style: solid;
 }
+
 [dir="rtl"] .ckeditor5-toolbar-button-heading::after {
   margin-right: 0;
   margin-left: 10px;
diff --git a/core/modules/ckeditor5/css/language.admin.css b/core/modules/ckeditor5/css/language.admin.css
index 42ebab47e99b3411a2b94070543587d03f3a4978..cb9997852bfd6d2dff7352c628d79f1677ea6063 100644
--- a/core/modules/ckeditor5/css/language.admin.css
+++ b/core/modules/ckeditor5/css/language.admin.css
@@ -5,15 +5,20 @@
   width: 110px;
   color: #000;
 }
+
 .ckeditor5-toolbar-button-textPartLanguage::before {
   margin-left: 10px;
+  /* For browsers which don't support alt content, eg FireFox */
   content: "Language";
+  content: "Language" / "";
   font-size: 14px;
 }
+
 [dir="rtl"] .ckeditor5-toolbar-button-textPartLanguage::before {
   margin-right: 10px;
   margin-left: 0;
 }
+
 .ckeditor5-toolbar-button-textPartLanguage::after {
   display: inline-block;
   width: 7px;
@@ -24,6 +29,7 @@
   border-width: 2px 2px 0 0;
   border-style: solid;
 }
+
 [dir="rtl"] .ckeditor5-toolbar-button-textPartLanguage::after {
   margin-right: 0;
   margin-left: 10px;
diff --git a/core/modules/ckeditor5/css/style.admin.css b/core/modules/ckeditor5/css/style.admin.css
index 6cb5b6bd5303dcc122c913593f889e70727f4901..add5dbabd38042dc5e9fa9eaf0361fb24bb17de6 100644
--- a/core/modules/ckeditor5/css/style.admin.css
+++ b/core/modules/ckeditor5/css/style.admin.css
@@ -5,15 +5,20 @@
   width: 110px;
   color: #000;
 }
+
 .ckeditor5-toolbar-button-style::before {
   margin-left: 10px;
+  /* For browsers which don't support alt content, eg FireFox */
   content: "Style";
+  content: "Style" / "";
   font-size: 14px;
 }
+
 [dir="rtl"] .ckeditor5-toolbar-button-style::before {
   margin-right: 10px;
   margin-left: 0;
 }
+
 .ckeditor5-toolbar-button-style::after {
   display: inline-block;
   width: 7px;
@@ -24,6 +29,7 @@
   border-width: 2px 2px 0 0;
   border-style: solid;
 }
+
 [dir="rtl"] .ckeditor5-toolbar-button-style::after {
   margin-right: 0;
   margin-left: 10px;