When applications send a URL string to the File Manager application they scramble the URL into something that looks like a file path.  For example, if an application sends "http://www.google.com" to the "Preferred Applications - File Manager" then it will scramble the URL and send the following to the File Manager application:  "/home/username/http:/www.google.com".  Now granted, the application could send the request to the "Web Browser" handler but it doesn't and also if you run `thunar "http://www.google.com"` on the command line it handles the request just fine by deferring to the "Web Browser".

I don't know that this is necessarily a "thunar" bug since thunar receives the scrambled URL but one of the devs would probably know better where to file this issue.

You can see this if you put the following script in place of Thunar in the "Preferred Applications - File Manager" settings:

[code]
#!/usr/bin/python

import sys
import os

input = sys.argv[1]

if ('http:' in input):
    url = input
    os.system('echo "%s" > badlink.txt' % url)
    os.system('leafpad badlink.txt')
else:
    os.system('thunar "%s"' % input)
[code]