https://www.facebook.com/INVITE-ALL-FRIENDS-SCRIPT-2011-101029569982725/
Go to the Event page
Confirm your attendance
Put INVITE FRIENDS
Scroll down to your last friend (beginning with Z or some sign)
Copy from here this code
javascript:elms=document.getElementsByName("checkableitems[]");for (i=0;i<elms.length;i++){if (elms[i].type="checkbox" )elms[i].click()};
Chrome or IE -
go to adress field(where you write www.google.com), delete all what is there and put CTRL+V, then go to start of the line (with arrow left) and write in the front of code "javascript:" without quotation marks
Mozzila -
Open Web developer console and put CTRL+V
