I'm using the Chrome version and I very much like it. There are a couple of bugs though:

1) On the achievement comparison page (compare friends stats to yours), the achievements are listed twice. Reproduce by going to a friends profile page, click on a "achievement progress" for a game recently played that you also own, click at top "compare these stats to your own".

2) On the activity page there are three links (Compare) that are identical for a "<friend> achieved <game>: <achievement icon list>"