As Slack rapidly grows, its approach to keeping users in one place increasingly looks like Facebook’s. The same way that Facebook doesn’t want you straying into the wilds of the open web to read a news article that one of your friends posted, Slack doesn’t want you heading over to Tumblr to search for the perfect reaction GIF for your Slack chat. So where Facebook has Instant Articles (which allow users to read outside articles from within Facebook), Slack has integrations with companies like Riffsy, which offers a smattering of GIF options when prompted by a Slack command (kind of like the Giphy command in Slack, but without the terrifying roulette quality).
The real question is why you’d want to use Slack in the first place. Not everything is urgent, and the tool’s implied need to be “always on” undermines rather than reinforces productivity.