Just had it popping-up while accessing the site as usual, using Chrome on Windows 10.
Downloading suddenly in progress, stopped it and exited the site as advised above.
Re-accessed the site one more time again, logged-in, no trace of the Java 8.0 pop-up this time.
By the way, I had already logged-in to the site at least twice earlier today, after this thread had already been started, and no problem with pop-ups then.
Why I got it now is a mystery.