Delphi control that could mimic "Add-ons|Extension list" of Firefox?

You can do something similar (not exactly) with standard components; TDBCtrlGrid, TSpeedButton,...

alt text http://img8.imageshack.us/img8/9585/imagen29ox3.png

If you're using Delphi 2007 or Delphi 2009, you might be able to do something similar using TCategoryButtons (from the 'Additional' component palette page). Drop it on a form and right click to display the popup menu, and then click "Categories Editor...". Add a category with the resulting dialog, set it's caption, and optionally set up Items it contains. Not exactly the same, but it might do what you need.

You could also use a dialog with a TTreeView (if you have categories of objects) or TListView to emulate the Delphi 2007 Projects->Options dialog. Clicking an item in the TreeView or ListView displays the proper page of a TPageControl to configure the object.

Using a TFrame for each list item and put them all Aligned Top on a TScrollBox might work. Also see TDBCtrlGrid which does something like that in combination with datasets.