diff --git a/mozilla/layout/html/document/src/ua.css b/mozilla/layout/html/document/src/ua.css
index f882ee32c8d..43fe0a694ee 100644
--- a/mozilla/layout/html/document/src/ua.css
+++ b/mozilla/layout/html/document/src/ua.css
@@ -310,6 +310,9 @@ OBJECT {
 }
 HR {
   display: block;
+  margin-top: 0;
+  margin-bottom: 0;
+  text-align: center;
 }
 BR {
   display: inline;
diff --git a/mozilla/layout/style/ua.css b/mozilla/layout/style/ua.css
index f882ee32c8d..43fe0a694ee 100644
--- a/mozilla/layout/style/ua.css
+++ b/mozilla/layout/style/ua.css
@@ -310,6 +310,9 @@ OBJECT {
 }
 HR {
   display: block;
+  margin-top: 0;
+  margin-bottom: 0;
+  text-align: center;
 }
 BR {
   display: inline;