I have created images of navigation bars and others using Fireworks CS6. However, I notice that selecting a navigation bar does not allow your to crop that image using Crop Selected Bitmap on the Edit menu. Please someone advise me how to crop an image in precise size from Fireworks so that I get a navigation bar in the ideal size I want.
Not sure if my answer is what you are looking for but here goes.
You can crop/delete any part of a bitmap by using the marque tool, I think the default shortcut key is the M key.
Another tip - using the marque tool you can select areas of your bitmap then go to Select (menu) then select inverse... now when you select the delete key it will delete everything outside of the selected marque.
A little more advanced but extremely useful:
The way I work in FW is a bit different. I alsmost never use bitmap graphics, rather I use vectors. Using these handy, quick custom commands that I created http://fireworksinstructionalvideos.com/commands/selectPoints.zip, you can resize any object from any side with a simple shortcut key.
Once you have these four commands installed you can set up some really useful shortcut keys:
Left - shift + alt/option + L
Right - shift + alt/option + R
Top - shift + alt/option + T
Bottom - shift + alt/option + B
I hope this helps!