You don't have to install the latest Mozilla to block popup messages. Just go into your default installed Mozilla and click Edit->Preferences->Advanced->Scripts&Plugins then uncheck the "Open unrequested windows". Better yet, install the
Prefbar so you can just turn it off by clicking a checkbox right on a menu bar. I know that doesn't answer your question about how to upgrade to the latest Mozilla that is not yet in the apt repository but I haven't found a reason to make such an upgrade to the bleeding edge.
