diff --git a/toolkit/content/widgets/notificationbox.js b/toolkit/content/widgets/notificationbox.js
index f4e95470aea5..bef4fce077e2 100644
--- a/toolkit/content/widgets/notificationbox.js
+++ b/toolkit/content/widgets/notificationbox.js
@@ -734,7 +734,7 @@
               "button",
               button.is ? { is: button.is } : {}
             );
-            buttonElem.classList.add("notification-button", "small");
+            buttonElem.classList.add("notification-button", "small-button");
 
             if (button.primary) {
               buttonElem.classList.add("primary");
diff --git a/toolkit/themes/shared/in-content/common.inc.css b/toolkit/themes/shared/in-content/common.inc.css
index 39b739f22b26..227247564a37 100644
--- a/toolkit/themes/shared/in-content/common.inc.css
+++ b/toolkit/themes/shared/in-content/common.inc.css
@@ -356,15 +356,9 @@ xul|menulist {
 button {
   font-weight: 600;
 }
-/* Medium and small buttons get sized to 7/14 and 6/12px padding (when adding
- * the 1px border): */
-button.medium {
-  padding: 6px 13px;
-  min-height: 28px;
-  font-size: 0.95em;
-}
 
-button.small {
+/* Small buttons get sized to 6/12px padding (when adding the 1px border) */
+.small-button {
   padding: 5px 11px;
   min-height: 24px;
   font-size: 0.9em;