Adding target="_blank" to form will post & open the result in a new tab (or window).
<form target="_blank" enctype="multipart/form-data"
action="https://www.example.com/" method="POST">
<!-- more HTML -->
</form>
// and from the addon form.submit();
// there isn't any button or link to be clicked by the user
By default, the new tab will be the selected/foreground tab.
Is it possible to control/set the foreground/background status of the new tab?
N.B. The purpose is to give the USER the choice of opening in the foreground or background by using a modifier key (like for example shift or Ctrl).
The code is part of a Firefox addon (not part of site JavaScript).