diff --git a/layout/html/document/src/html.css b/layout/html/document/src/html.css
index 2f50ba16be34..3f506d9b0013 100644
--- a/layout/html/document/src/html.css
+++ b/layout/html/document/src/html.css
@@ -226,7 +226,7 @@ q:after {
 }
 :link:focus, :visited:focus, :out-of-date:focus,
 :link:focus img, :visited:focus img, :out-of-date:focus img {
-  outline: 1px dotted black;
+  mozoutline: 1px dotted black;
 }
 :link:active, :visited:active, :out-of-date:active {
   color: red;
diff --git a/layout/style/html.css b/layout/style/html.css
index 2f50ba16be34..3f506d9b0013 100644
--- a/layout/style/html.css
+++ b/layout/style/html.css
@@ -226,7 +226,7 @@ q:after {
 }
 :link:focus, :visited:focus, :out-of-date:focus,
 :link:focus img, :visited:focus img, :out-of-date:focus img {
-  outline: 1px dotted black;
+  mozoutline: 1px dotted black;
 }
 :link:active, :visited:active, :out-of-date:active {
   color: red;