The updates take both products to version 188.8.131.52, and were issued via the vendor's automatic update system this morning, Australia-time.
The less popular SeaMonkey mail and browsing suite was also updated to version 1.0.5.
Mozilla's Web site lists security-related fixes for Firefox, including a bug showing evidence of memory corruption, and other holes that could be exploited by malicious attackers. Many of the issues were pointed out by parties external to the vendor.
Thunderbird was updated to correct many of the same issues.
According to SpreadFirefox, a marketing and promotional Web site for Firefox, the browser has been downloaded more than 216 million times.
Thunderbird is a little less popular, with close to 32 million downloads since its official 1.0 release, according to a Weblog chronicling development of the software.
Meanwhile, the next major release of Firefox, version 2.0, is due in late October.