I'm always asked to opt in here

The canonical entry point for DevForums is https://developer.apple.com/forums. If you start out at https://forums.developer.apple.com you will encounter weird problems. DevForums really should redirect the latter to the former (r. 132309185).

Unfortunately there are a lot of forums.developer.apple.com URLs out there in the wild. When I get them I remove the forums. prefix by hand and things go a lot more smoothly.

Share and Enjoy
—
Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

I get the same behaviour using https://developer.apple.com/forums -- just repeated several times in a row, by logging in in this window, then opening a new window and pasting https://developer.apple.com/forums into the address bar.

So that's not it.

OK.

Last I checked this setting was stored locally in one of the website local data stores (Local Storage IIRC). Are you sure your browser is preserving that?

Share and Enjoy
—
Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

I've no idea why it wouldn't. It's Safari. I even (just now) turned off content blockers for this site, and it still does this. How would I figure that out?

(I have a couple of ad blockers, TamperMonkey, and 1Password as installed & active extensions.)

How would I figure that out?

With web inspector.

Share and Enjoy
—
Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

Which is beyond my (current, at least) capabilities. sigh.