Strange pop up requesting login details

[notquitegrownup2]

Was trying to read MN on Firefox and a pop up kept appearing looking a lot like the key bit of the MN login page. No way of getting rid of it nor of reading on, without using it to log in. It blocks the way to reading on, greying out the back screen, and also blocks access to the proper logon page.

Switched to IE and I can get in fine, so am using that to report it. Suspect that it is something dodgy and not to be used.

Hiya - this sounds like part of something we're testing, there's a full explanation here. Does that seem to match with what you're seeing?

Yes, that's it.

Thanks