Adding back default firefox

the default is triggered only outside the case statement, which itself
is totally bizarre. I can't tell if anyone is relying on this behavior
right now, but it's too premature to just remove it out at this point.

Author: Tod Beardsley

lib/rex/compat.rb

@@ -145,6 +145,9 @@ def self.open_browser(url='http://metasploit.com/')
 				end
 			end
 		end
+
+		# If nothing else worked, default to firefox
+		system("firefox #{url} &")
 	end
 end