> Everytime I run webhttrack it opens "Mozilla Suite" not
> Firefox who is the Fedora default browser

The default might not be set correctly - that is:
- by the 'sensible-browser' executable (if any)
- by the 'x-www-browser' or 'www-browser' executable (if any)
 
Try to start 'sensible-browser', 'x-www-browser' or 'www-browser' to see if
the correct browser is launched.

You may also set the BROWSER variable in your ~/.profile:

BROWSER=/usr/bin/firefox
export BROWSER