[fix bug 1038734] Adjust tour menu panel highlight timing

The menu panel in Nightly now animates when it opens, which means we need to use a slight delay on the web page when telling the panel to open before highlighting an item.

https://bugzilla.mozilla.org/show_bug.cgi?id=1038734

Note: I've switched to using `setTimeout` here instead of jQuery `delay()` as it turns out it doesn't actually work on event triggers :smile: