Stored XSS in Slack.com

How it was found

Steps:

Go to your respective URL Mine is https://dezignburg.slack.com/account/photo

now Change your photo using Facebook

But before that create a Album in your Facebook naming it as "><img src=x onerror=alert(document.cookie)>

And you will get this error: http://prntscr.com/37eecd

If you need a video just tell me