I take it you use Firefox version 52?
With the newest Update, Firefox now warns, if you log in to a site that does not use encryption to send your password. This is the case with pages that start with http instead of https. Since the password is sent in plain text, it is theoretically possible for hackers to wiretap the connection and steal your password. Chances that someone really does it are slim, but who knows?
What to do about it? Well neither you nor I can do anything about it. It would be up to Saj, our Forum host to install a security certificate on the server the Forum is hosted on.
Is the connection less secure than it was before? No, it is just the same as always, but now you are being made aware that this website uses no secure connection to send your password to the server.