To install simply change the email address in contact.php and copy and paste the code from index.html between and tags on to your website.
If your contact.php file is in a different directory to your webpages make sure you update line 21 to include the full url like: var feedbackform_url = 'http://mywebsite.com/contact.php';
Example: http://JamesBachini.com/misc/feedbackexample.html
There are no dependancies so it should work anywhere.
Original post: Simple Floating Feedback / Support Button Form
Tested on Firefox, Chrome and Edge.