R1:49a7f9e7d77f

Fix download button to work on firefox

Summary: need to setTimeout on the removal from the DOM so these browsers don't freak out

Test Plan: downloaded images on firefox and safari

Reviewers: vrana, epriestley

Reviewed By: vrana

CC: aran, Korvin

Maniphest Tasks: T1896

Differential Revision: https://secure.phabricator.com/D3799