Fireworks offers tools to quickly and easily size and optimize web images - I recently took on redoing an older web site for practice and was horrified to discover the designer had provided large images of various sizes for the site. Each time the site was viewed, the browser was forced to resize every image on the fly - shoehorning them into thumbnails in table cells. Fireworks made short work of creating a set of decent thumbnail images and converting the odd jpeg to gif to allow some transparency (I skipped using png files so older browsers wouldn't have problems).
Like Flash and Dreamweaver, also acquired when Adobe bought Macromedia, Fireworks has a GUI that is somewhat different than the traditional Adobe programs. Some of the image adjusting tools, like curves, look much like those in older versions of Photoshop, while other tools are unique to Fireworks.