diff --git a/toolkit/themes/pinstripe/mozapps/update/updates.css b/toolkit/themes/pinstripe/mozapps/update/updates.css
index 69cff7e738f7..a63943e32029 100755
--- a/toolkit/themes/pinstripe/mozapps/update/updates.css
+++ b/toolkit/themes/pinstripe/mozapps/update/updates.css
@@ -75,7 +75,7 @@ wizard[currentpageid="updatesfound"] .wizard-page-box {
 }
 
 #incompatibleCheckingThrobber {
-  margin-right: 4px;
+  -moz-margin-end: 4px;
   background-color: transparent;
   list-style-image: url("chrome://global/skin/icons/loading_16.gif");
 }
diff --git a/toolkit/themes/winstripe/mozapps/update/updates.css b/toolkit/themes/winstripe/mozapps/update/updates.css
index afefed95f0c4..8c0aa21fbc0e 100755
--- a/toolkit/themes/winstripe/mozapps/update/updates.css
+++ b/toolkit/themes/winstripe/mozapps/update/updates.css
@@ -62,7 +62,7 @@ license {
 }
 
 #incompatibleCheckingThrobber {
-  margin-right: 4px;
+  -moz-margin-end: 4px;
   background-color: transparent;
   list-style-image: url("chrome://global/skin/throbber/Throbber-small.gif");
 }