While using Firefox, any client script / Catalog client script comparing or 'newing up' a date from a date picker in the platform are either not running or not working as expected.
Firefox is not as flexible in formatting dates as Chrome or IE
Follow the documentation within Firefox for proper formatting before making a new date.
This is an example of what would be invalid versus valid that was tested in the console of Firefox's console
var dateFail = new Date('09-11-2018'); // This is a common date format a date field in Service Now
dateFail returns -> Invalid Date
var newDate = new Date('2018-09-11');
newDate returns -> Date 2018-09-11T00:00:00.000Z
If you are following the formatting properly and the client script is not working properly, please open a ticket in HI referencing this KB article.