How to use Javascript Debugger when javascripts was obfuscated

[email protected] Wed, 8 Apr 2009 02:58:30 -0700 (PDT)

Newsgroups	gmane.comp.mozilla.devel.jsdebugger
Organization	http://groups.google.com
Message-ID	<08b0a818-9f56-4f66-aef4-6d85a9774785@z19g2000vbz.googlegroups.com>

 I found the following  Javascript code.

(All Javascript code is displayed at one line:)
function mj67(sdadad21){sds("%3B%66%6F%72%28%76%61%72%20%6E%4B%39%36%3z
%30%3B...

I guess the Javascript code is malign,but I don't sure.
I want to use Javascript Debugger to debug it,but all code is at the
same line,I don't know how set the breakpoint.

Could some one give me a hand?