Down the FAQs for browsers:
Opera v 47.0.2631.71
No ad-ons running.
This site's always given me a bit of trouble, in that the "remember me" function has never worked, but I didn't care much about that in the first place.
Now (re: started approximately half an hour ago) it won't log me in at all. Whenever I click login, it brings me to the screen, I log in, and it goes back to the main site... where I am still not logged in.
Cookie Purge didn't help.
Login appears to be working normally with Internet Explorer, which I'm currently using.