in CS5 you could find it under the command tab but now it is gone
That command was removed from Fireworks CS6, and listed among the deprecated features in this Adobe blog post:
http://blogs.adobe.com/sarthak/2012/06/fireworks-cs6-new-feature-list. html
If you still have the CS5 version, you might try copying it over to CS6; perhaps it will still work.
North America
Europe, Middle East and Africa
Asia Pacific