<br /> Instagram cofounders Kevin Systrom and Mike Krieger announced they were quitting Facebook on Monday, but snubbed Facebook CEO Mark Zuckerberg in their goodbye letter. The pair did eventually mention Zuckerberg in an Instagram post, along with a few other Facebook executives. This is not the first time a founder has snubbed Zuckerberg in announcing their departure — WhatsApp's Jan Koum also made no mention of the Facebook CEO when he left in April. Instagram's cofounders Kevin Systrom and Mike Krieger announced they were leaving Facebook on Monday night amid reports of tension with Facebook CEO Mark Zuckerberg. <br />