The one I'm using is "Tenfourbird 38.9.0 for PowerPC 7450" with a 7/14/16 creation date. Is that the one you found? Unfortunately I didn't bookmark where I found it. I was under the impression it could automatically use the latest security from TFF even if it is a few years old.
Unfortunately, no, it can't. One of the good and bad things about Mozilla-based apps is that they are self-contained. This allows TenFourFox to have updated security without affecting the rest of the system or requiring installing additional components, but it's bad in that no other applications, even other Mozilla-based ones, will benefit from them.
I see. Well I'm still going to keep on using it because it's surely at least as secure and with more features than any other email app that will run on a PowerPC running Tiger (that old SweetMail app I was using won't even display HTML-based pages).