The gap in security your browser is pointing out is common on most sites, but Chrome/FireFox has decided to start highlighting it now. It's telling you that the site is vulnerable to a MIM attack (or Man in the Middle), where someone intercepts what you are typing on the site. Since everything you type here is view-able to all, this has never been a thing it made sense to protect against. As long as you aren't typing your password into a thread in plain text, or your bank info, this doesn't affect you.
All that said, we are going to be upgrade all our network over the coming months to HTTPS to make our pages secure.
Indeed it is a certificate. Unfortunately, while it is as simple as 'flipping a switch' to turn it on, the road to get to that point is far from simple. From several thousand domains, on top of second and fourth level domains; user submitted content; ad networks; all the sites and apps communicating via APIs; there are a lot of moving pieces to consider as tech puts this in place, to ensure a smooth transition and no interruption to your enjoyment of these communities.
We do realize the importance of SSL, and it is something we are working towards though there are no official ETAs on release as of yet.