The main goal in web graphic design is to create good looking images that download as fast as possible. To do that, you must choose a file format with the best compression for your image while maintaining as much quality as possible. This is called optimization - getting the right mix of colour, compression, and quality.

There are 3 main graphic formats that you can use on web pages. .jpg and .gif are the most common, with .png becoming more common.  Although Fireworks saves its files in .png format, this is a different .png format to that used on the web.  Fireworks includes extra information that isn't relevant to the web.  If you want to use a .png file on the web, you should export it to a regular .png file.

Fireworks has special tools that help you to compress your images as much as possible without losing too much quality so that they load quickly on the web.

This video will show you how to optimise an image using Fireworks