If you have a default install of bluefish on Fedora 7. It is probably configured to use mozilla as the default browser and may have some rather complex command line to launch a browser and display the file you are working on.

exo-open from the XFCE4 project takes a URI argument and handles all the intricacies of launching the browser for you.

Go into bluefish
Select Edit => Preferences
Select External Programs
Under the browser field delete the Browsers that aren't installed on your system
Add an entry named exo with a value of exo-open %s

You should now be able to click "External => Exo" to open your default browser as configured from the XFCE4 preferred applications program