Mozilla 1.6 starting mode

Hi !

My problem is that:
I use Opera before Mozilla in Windows. Opera is always open new tab for 
http://xxxx request of applications, example: when I click a http addr. 
in mail, or run from shell a "start http://xxxx" command.

But Mozilla 1.6 is use the last opened window to it, what very unuseful 
- it is "drop" my previous web address.

In Preferences page I see GroupBox with a combobox with 3 options:
- Start browser
- In New Window
- In New Tab
and some radiobuttons:
- Empty page
- Homepage
- Last visited

This combobox is uneditable, when I modify it (change to New Window), it 
is forget the parameters.
In prefs.js I cannot see any option to set it.

How to I do it ?

How to change this option to Mozilla open the request in new Window ?

Thanx for every help:
FT