Thanks Xavier for Reply.

I'm supernewbie in Linux, I think that 'x-www-browser' or 'www-browser' isn't
for Fedora , it is for Debian or other distros.

But after   reading the file /usr/local/bin webhttrack I see that the variable
:
SRCHBROWSEREXE="x-www-browser www-browser mozilla firefox firebird galeon
konqueror opera netscape"

maybe is the problem. I simply change the order I put:
....firefox mozilla .......

First firefox than mozilla ..and Now it works!!!! I'ts great now webhttrack
open in Firefox......

Thank you very much