Title says it all. Same website (only tried one so far) has worked with Firefox on this Ubuntu install, works on my phone and works on Windows based PCs. A little pop-up window (the login window) appears briefly but it does not log me into the website!
Noticed on this site: https://www.firezza-orders.com
Running Ubuntu Studio 16.04
Opera ver 47.0
Do you use adblock (the built in or some addon) or you have third party cookies disabled?
Yes I've been using the inbuilt adblocker. I use AdBlock Plus on the other systems, which seems to use the same block lists though. The other systems also have third party cookies disabled and work.
Facebook login just worked on a different site though, after allowing popup (although with the site mentioned above I saw the Authentications popup open and close) so it definitely isn't a systemwide problem.
Think it was the third party cookies. Tried disabling each thing that may have conflicted in turn and it eventually worked. Weird that it works in Firefox at this website with third party cookies disabled, and it works with Opera on other sites. Anyway I think I can live with leaving it set to accept all cookies...