Just install Chrome, the GUI interface is supposed to load in a browser and
maybe we miss some add-ons in Firefox. You might have problems in running
Chrome as root, so after the installation you should first make a copy of the
original google-chrome file:

cp /opt/google/chrome/google-chrome /opt/google/chrome/google-crhome-orig  
 
Then edit the original:

gedit /opt/google/chrome/google-chrome

Go to the very last line and change: 

exec -a "$0" "$HERE/chrome" "$@" 
to 
exec -a "$0" "$HERE/chrome" "$@" --user-data-dir $HOME 

Save the file and be sure that its permissions are -rwxr-xr-x and that the
owner and group is "root". 

Try to run the webhttrack GUI interface. 

This worked for me.