We encourage all users to update to 0.5.2.
0.5.2 adds support for Firefox 5, Firefox 6, and the latest versions of SeaMonkey.
With the Gmail S/MIME extension, you can send and receive signed and encrypted S/MIME messages in Gmail. Secure your e-mail today, including your attachments! Version 0.5.2 inter-operates with every S/MIME-capable mail client including Microsoft Outlook (2000-2010), Microsoft Outlook Express, Mozilla Thunderbird, and Apple Mail.app, and now works up through Firefox 4.0, Seamonkey, and the latest versions of Gmail.