The file extension STL identifies style libraries, ie style libraries of the graphic editing software Adobe Fireworks. These styles can be selected from the Styles window and applied to images or pels. A style usually includes color changes, filters and margin settings.
The standard STL files 'Styles.Stl' and 'Styles Defaults.Stl' are stored in the Fireworks folder under 'First Run / Styles' or 'First Run Nav Menu'. In addition, you can also create new styles in the style window and import and export STL files via the icon on the top right.