TitanSnow, 

You're right, sorry about the confusion.

But, nevertheless, this does seem to be something that the browsers don't have available as an option.

Here's the Mozilla command line option page:
https://developer.mozilla.org/en-US/docs/Mozilla/Command_Line_Options

Under the Browser section, there is a note stating:
Note: When opening multiple URLs, Firefox always opens them as tabs in a new window.

I believe the other browsers behave the same.