Each tab modifies settings in the relevant area, the toolbar hacks tab for instance has a setting to combine the stop and reload buttons, show only icons in the bookmarks toolbar or hide the search bar except for the site icon until the user hovers his mouse over it. I used most of the settings to change the appearance of my firefox and make it more compact, remove unwanted features that I was never using was my priority.

The extension has a feature for multi-row bookmarks toolbars but this option is greyed out in my extension. The author claims it is a firefox bug which makes it work only sometimes. Try for yourself and see if you get this to work, would be nice to have more than one toolbar with bookmarks.