Add Google Calendar Event Bookmarklet

gistfile1.js

javascript: var s;
/*Figure out the selected text*/
if ( window.getSelection ) {
    s = window.getSelection();
} else if ( document.getSelection ) {
    s = document.getSelection();
} else {
    s = document.selection.createRange().text;
}
/*If there isn't any text selected, get user input*/
if ( s == '' ) {
    s = prompt('QuickAdd');
}
var re = RegExp( '[AaPp][Mm]' );
if ( encodeURIComponent(s).match(re) ) {
} else {
        var d = new Date();
        var hr = d.getHours();
        var min = d.getMinutes();
        if (min < 10) {
                min = "0" + min;
        }
    s = s + " " + hr + ":" + min; /*if there isn't an AM or PM in the text, add the default current time*/
}
void(
/*open a new window with this information in the Google Calendar event creation page.*/
    window.open(
        encodeURI('http://www.google.com/calendar/event?ctext='+s+'&action=TEMPLATE&pprop=HowCreated:QUICKADD'),
        'addwindow',
        'status=no,toolbar=no,width=520,height=470,resizable=yes'
    )
);

It seems Google has made it so that this bookmarklet does not work anymore while browsing mail.google.com, it works if you are browsing any other website.
Tried using Firefox v55.0.3, new profile, all default settings.

It would be highly appreciated if you could fix this useful bookmarklet @ajsharma