If you are using FireFox - switch to Chrome, IE, Safari, Opera until further notice. This reportedly impacts Tor Browser and FF v45-50.
If you don't know what I am talking about but use Firefox, stop and switch for a while.

No Tor? How am I supposed to order illegal guns, drugs and snuff films now
Posted from my iPhone/Mobile device

Hahaha - do it how we did it before the Internet - go to the Adult Store and order your Mr Peepers the old fashioned way

This affects nobody other than those running Windows that use the Tor Project’s anonymizing TorBrowser within Firefox.

So i only use firefox since that's where everything is bookmarked. How long are we supposed to avoid firefox? And am i safe with Norton running?

Until a patch is available, Firefox users should use an alternate browser whenever possible, or they should at the very least disable JavaScript.

Link to more detailed article on this issue (http://arstechnica.com/security/2016/11/firefox-0day-used-against-tor-users-almost-identical-to-one-fbi-used-in-2013/)

I hope you'll let us know when its safe to go back to firefox.

Update at 2:32pm PST / 5:32pm EST: Firefox released a fix for this a few minutes ago. Update to Firefox 50.0.2 now to patch this vulnerability. Tor have also released a fix with version 6.0.7 of their browser.There is also a Thunderbird fix out, version 45.5.1. I also posted an extended update at the end of the post including data indicating this exploit may be part of a law enforcement operation.

/End Update.