I've been using a very old version of Photoshop and as a web designer I mostly use Image Ready when editing images for sites. One of my most used features is crop & scale - if I have a 2000px by 1000px image I can specify that I want a 250px square crop and the cropping outline will maintain the aspect ratio while I position it. I can drag the bounding box to the full height of the image and I'll end up with a 250px square image. When I specify a crop size in Fireworks it just allows me to crop that size regardless of the image size. Is there a setting somewhere that I'm missing?
In Fireworks, you have an image size, and a canvas size at the bottom, in the property inspector. They are separate for a reason and that way on purpose. There are a variety of ways to scale. Always best to scale the image first, then "Fit Canvas" in the property inspector.