NSM certificate prompt

[Eli Zaretskii <eliz@gnu.org>]

If I use eww to connect to www.google.com and then click on the "Sign
in" link, I get the following buffer displayed to me by the NSM:

  Certificate information
  Issued by:          Google Internet Authority G2
  Issued to:          Google Inc
  Hostname:           accounts.google.com
  Public key:         RSA, signature: RSA-SHA1
  Protocol:           TLS1.2, key: ECDHE-RSA, cipher: AES-128-GCM, mac: AEAD
  Security level:     Medium
  Valid:              From 2014-12-03 to 2015-03-03


  The TLS connection to accounts.google.com:443 is insecure for the
  following reasons:

  certificate signer was not found (self-signed)
  certificate could not be verified

This is in Emacs 25.0.50 built with GnuTLS 3.3.11 on MS-Windows.
Other Web browsers on this system don't have any trouble displaying
that page.  Do others see this on other systems?  Is my system/Emacs
somehow misconfigured wrt certificates?

TIA