The one thing that bothered me enough (apart from hiding the top tabbar with the userChrome changes mentioned in another review) is the fact that the tabs are padded too much for my taste.
Luckily there's a "Extra style rules for sidebar" textarea in the options page, where you can put extra CSS rules for the sidebar. I've added the following in that textarea: /* slimmer tabs in sidebar */ .tab { padding: 1px; }
