Fireworks tool set and workflow is designed for Web layout. Photoshop's tool set and workflow is designed for image editing. Yes, over the years, Photoshop has had more Web tools added and Fireworks has had more image editing and effects tools added, but the basic philosophy of each application remains the same.
If you use Fireworks for what it's intended - and get good at it - you'll probably find that you are more efficient at producing Web layouts than you are when using Photoshop. The workflow is different, the approach is different, some terminology is slightly different (layers and sub-layers, for example, are used to organize objects, which can be vectors or bitmaps).
I've seen people try to approach Fireworks as some kind of "Photoshop Limited," which it isn't. (These people are often very frustrated by FW.) Fireworks is a different application with a unique, hybrid approach to layout, design, and export. It was never intended as a general-purpose image-editing application. The underlying, basic assumption with Fireworks is that you will use it to design a Web layout and produce Web graphics (plus some other things). Consequently, all the essential tools and menu commands you need for these tasks are integral to the application and easily accessed.
Here are a couple of links:
A tutorial link for Fireworks as well:
I use PS for two things: doctoring photos (brush, clone stamp, magic wand, etc.) and for creating graphics from the huge selection of custom brushes, shapes, etc. that you find on the web. Otherwise, FW is the choice for all web graphics. Once you get used to it, you'll wonder how you were ever able to deal with PS...