Firefox would never show such a message.

If you get a pop-up message asking to update Firefox or plugins or scanning for malware then such a message is likely a scam and you should never respond to such an alert to avoid getting infected with malware.

• Only update Firefox via "Help > About" or by downloading and installing Firefox from the Mozilla server and never via a pop-up or link on a web page.
• Plugins should only be updated via the plugin itself or by visiting the home page of the plugin
  https://www.mozilla.org/plugincheck/

I also received a "FireFox Patch" today...saved, not run.. marked eivaeciplex.net, and identified in properties window as Wintime Check.