1.) Right-click the Titanfall box art.

2.) Click 'Game Properties' on the newly opened context menu.
3.) In the Game Properties window type in the following:
+cl_showfps 1 -novid -noborder

4.) Click 'Apply'.
*note: the '-noborder' command makes alt-tab quicker, and has nothing to do with windowed mode. Commands can be left out or added, just be sure to leave a space between them.