One way to do it (not just for Mozilla) is to set up URPMI and use that.
(I think - anyone correct me if I'm wrong - that mandrake update is only from Mandrake itself...so if they don't release their own updates, you're SOL until they decide to include it...again, I might be wrong on that score)
To set up URPMI, a really easy way is to go to this site and follow the instructions:
http://plf.zarb.org/~nanardon/
You can also search this site for specific issues if you have a particular problem, but the above site will give you a nice list of software sources.
Once you do that, you can just go to the command line as root and:
urpmi mozilla
and if there's a new version, it will all get updated for you. (use 'man urpmi' for details, I might have missed an option there)