Start desktop notification closing timeout only after they appeared.

src/Monitoring/Unread.coffee

@@ -104,6 +104,7 @@ Unread =
     notif.onclick = ->
       Header.scrollToPost post.nodes.root
       window.focus()
+    notif.onshow = ->
       setTimeout ->
         notif.close()
       , 7 * $.SECOND

src/Posting/QR.coffee

@@ -122,6 +122,7 @@ QR =
     # Firefox automatically closes notifications
     # so we can't control the onclose properly.
     notif.onclose = -> notice.close()
+    notif.onshow  = ->
       setTimeout ->
         notif.onclose = null
         notif.close()
@@ -1108,6 +1109,7 @@ QR =
         QR.open()
         QR.captcha.nodes.input.focus()
         window.focus()
+      notif.onshow = ->
         setTimeout ->
           notif.close()
         , 7 * $.SECOND