I'm actually using Chrome and my bookmark is to the site, https://www.dfworkshop.net
I always enter the forum from the link in the right side of the site.
Now, the funny thing is, I just entered the forum, and came to this thread without logging in. But when I opened this link to the other thread you posted, the forum in the other tab opened with me logged in.
Reloading this tab after that, instantly logged me in as well. It seems the link to the forum in the main site is assigned HTTP instead of HTTPS, maybe? Because as I magically logged on, the "Insecure" message before the address in the address bar changed to a closed lock.