diff --git a/platform/firefox/vapi-background.js b/platform/firefox/vapi-background.js
index 4ceb2c3ca..f062a50fd 100644
--- a/platform/firefox/vapi-background.js
+++ b/platform/firefox/vapi-background.js
@@ -202,7 +202,7 @@ vAPI.browserSettings = {
             if ( this.originalValues.hasOwnProperty(key) === false ) {
                 continue;
             }
-            pos = key.indexOf('.');
+            pos = key.lastIndexOf('.');
             this.clear(key.slice(0, pos), key.slice(pos + 1));
         }
     }