A new variant of the problem has appeared this morning, using Chrome on Win 10 Pro.

Going to flyertalk.com/forum/usercp.php produces a full-size box, but all the links are dead. So the box can't be cleared and the FT content can't be accessed.

Going to flyertalk.com produces a small box that shows only the first line ("Required cookies"). It is not possible to scroll down this box, so the links to accept or reject cookies can't be reached. Without being able to do that, the FT content can't be accessed.

I dimly remembered a third behaviour that occurs when using the link sent out in thread activity emails. I went to BA to retire entire B747 fleet - and fortunately, this produced a full-size box with active links, so that I could then log in and post this.

Yes, I know that I could switch to an alternative browser instead, but Chrome isn't exactly a minority sport. This ought to be capable of working properly!