Comment 5 for bug 451160

That looks much better. Unfortunately I don't have time for a proper review now, but I have one suggestion. Look at the interface for adding recipients when composing a message in Thunderbird. Notice how you don't need to open a separate window to add a recipient. You could use a similar approach to eliminate the "Add Rule" window altogether: instead of configuring a new rule in a separate window, configure it inside a new row in the "Rules" list.