Thanks! You should also null out `panelEntry.timer` in disable because that's not a reference. also after line 115 (extension.js)

The `resetTimer()` function (after line 115) already nulls out `timer` if the timer is not running or expired. If the timer is running, it replaces it with a new timer. I'll null it in the `disable` function, right before the `destroy()` call. I must admit that this part of object-oriented JavaScript is magic to me, so I'll take your word on it that this is necessary.