Firefox 18 was sent to the release channel today by Mozilla. Included in the update are twelve (12) critical, seven (7) high and one (1) Moderate security update. Based on the extensive list of security updates, it is recommended that the update be applied as soon as possible. Included in the update is the revocation in trust of two TURKTRUST certificates.
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.
Additional information at Mozilla Firefox 18.0.0 Released With Critical Security Updates