Check all checkbox while setting FLS from Profile

Open your Browser
Press Ctrl + D to create a bookmark.
Click on Edit.
Enter Name as desired, eg: chkAll - ReadAll
In the URL Enter the code below, and
Click Save.
To Check All Read-Only Checkbox
javascript:(function(){var x = document.querySelectorAll(".readonlyCol input");for (var i = 0; i < x.length; i++) { x[i].checked=true;}})();
javascript:(function(){var x = document.querySelectorAll(".displayedCol input");for (var i = 0; i < x.length; i++) { x[i].checked=true;}})();
To UnCheck All Read-Only Checkbox
javascript:(function(){var x = document.querySelectorAll(".readonlyCol input");for (var i = 0; i < x.length; i++) { x[i].checked=false;}})();
javascript:(function(){var x = document.querySelectorAll(".displayedCol input");for (var i = 0; i < x.length; i++) { x[i].checked=false;}})();