Norton reporting intrusion attempts from Washington Post

Hi.  Today, every time I open the Washington Post's website, or click on any link within it, NIS reports that it has blocked an intrusion attempt, namely "IPS Alert Name - Web Attack: Exploit Toolkit Website 27."  While the attacker URL section is blank, the text says, "Network traffic was detected that matches the signature of a known attack.  the attack was resulted from C:\Program Files (x86)\Mozilla Firefox\firefox.exe.  NIS just gives me the notification, it does not block the page.

I have no such warning when I open the Washington Post in IE. 

NIS 22.6.0.142.  Windows 7.

Any ideas? Thanks.