The CanSecWest (http://cansecwest.com/) security conference is underway and Firefox fell along with others (http://h30499.www3.hp.com/t5/HP-Security-Research-Blog/Pwn2Own-2013/ba-p/5981157). However, Mozilla developers quickly diagnosed the issue, built a patch, validated the fix and the resulting builds, and Firefox version 19.0.2 has been sent to the release channels.
Update:
To get the update now, select "Help" from the Firefox menu at the upper left of the browser window, then pick "About Firefox." Mac users need to select "About Firefox" from the Firefox menu.