The update includes five (5) Critical, three (3) High, seven (7) Moderate and two (2) Low security updates. To get the update now, select "Help" from the Firefox menu at the upper left of the browser window, then pick "About Firefox."
Details of security updates, changes and known issues compiled in my blog post at Mozilla Firefox 28.0 Released with Critical Updates (http://securitygarden.blogspot.com/2014/03/mozilla-firefox-280-released-with.html).