Incorrect support for latin characters in some webs

[GoogleCodeExporter]

What steps will reproduce the problem?
1. Add a custom synchronization rule for FilmAffinity:
^http://www\.filmaffinity\.com/(en|es)/search\.php\?stext=(.*)&stype=all 
2. Search in FilmAffinity, for example, by "plutón":
http://www.filmaffinity.com/en/search.php?stext=plut%F3n&stype=all

What is the expected output? 
The search box should show "plutón"

What do you see instead?
It shows "plut%F3n"

What version of the product are you using?
v1.3.1

On what operating system?
Firefox 3.6.3 under Ubuntu Linux Karmic

Original issue reported on code.google.com by simon@simonbcn.net on 4 Apr 2010 at 12:32