You can type in a date in both chrome and firefox, I checked. The one thing that the datepicker will prevent by default though, is that it only allows characters which are valid in the current date format to be typed. So if your date format is "03/02/1980" then it will not allow any letters to be typed etc. only numbers and /.
If this is what you want to turn off, to allow all characters to be typed, then use this:
$( ".selector" ).datepicker({ constrainInput: false });
constrainInput set to false will allow anything to be typed.
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