When Slack links are clicked, a tab is opened in your browser which then redirects to Slack Desktop.
This addon closes those tabs after two seconds (which is pretty arbitrary, it could be a lot shorter).
The code almost certainly isn't optimal, it was a quick hack after work today.
This is pretty much a direct copy of https://github.com/cshields/zoom-tab-close, with a couple of mods to suit Slack.