Although the foundation's security page doesn't yet list exactly which bugs were fixed, Mozilla's director of engineering Chris Hofman said earlier this week the e-mail client was vulnerable to the same security bugs as were fixed yesterday in Firefox 1.0.5.
Some of those bugs could allow a remote attacker to take over a victim's PC or expose sensitive user data, according to Mozilla's alerts.
Mozilla is recommending that all users upgrade to the latest version of Thunderbird, which is also billed as containing stability improvements.
The news comes as Yahoo yesterday announced it had updated the test version of its Desktop Search product to include support for searching Thunderbird-based e-mail databases. The product had previously only been able to search Microsoft's Outlook and Outlook express clients.
Other improvements touted by Yahoo include a simplified user interface, and reduced download size.
Google updated its own desktop search product in March to support Thunderbird, while competitor Copernic's product also supports Thunderbird as well as Outlook.
News.com's Joris Evers contributed to this report.