we did this before when using pdfs but in our case we are using Flex and we do not want to call the web browser from the flex we need it from the workspace directly,
please see the attachment, when the user clicks complete we want to open the browser instead of submitting the form to the next step.
You cannot do that without customizing workspace.
I'm still wondering why do you need that? Could you please elaborate your requirements?
Or you may place a button within your flex form and open the browser window.