Running an URL from Alt+F2

[Doug Laidlaw]

With KDE, I could type an URL into the command runner and it would open my 
default browser.  With Xfce at present, I need to preface that with the 
browser command, "firefox."

Is there a way of associating URLs with a browser?  Associating an application 
with a file in Thunar is standard, but the command line is different, regardless 
of the desktop.  I think that I read somewhere about a launcher specifically 
for URLs?

TIA,

Doug.