Here is an example of calling a task flow in a new browser tab:
Hope this is useful in your case too.
Are you using go link or go button ?
If Yes so then go link or go button has one property called target frame which has following value :
_blank: The link opens the document in a new window.
_parent: The link opens the document in the window of the parent. For example, if the link appeared in a dialog window, the resulting page would render in the parent window.
_self: The link opens the document in the same page or region.
_top: The link opens the document in a full window, replacing the entire page.
Which will applicable in your case you can use .