On Thursday, April 28, Mozilla released security updates for Firefox, Thunderbird and Seamonkey.  Additional details are available at

http://www.mozilla.org/security/announce/2011/mfsa2011-12.html

Title: Miscellaneous memory safety hazards (rv:2.0.1/ 1.9.2.17/ 1.9.1.19)
Impact: Critical
Announced: April 28, 2011
Products: Firefox, Thunderbird, SeaMonkey

 

Fixed in: Firefox 4.0.1
Firefox 3.6.17
Firefox 3.5.19
Thunderbird 3.1.10
SeaMonkey 2.0.14