I agree that the OP is a good explanation of what the problem is, but I guess I don't agree that that first post is a good explanation of what to do about it. My problem with it is that the lineonce you hear of the new version, you go to their website, download and install it
hides a great deal of complexity. For example, Thunderbird just told me it will be obsolete in nine days. I can do the "go to their website, download" part just fine. I have no idea how to then install it, without losing all my old email, or breaking my account settings. Searching for "thunderbird linux update repositories", one of the links is to http://forums.linuxmint.com/viewtopic.php?f=197&t=86176
with nine steps, and I'm not even sure if I should follow them, because I don't know what LMDE means.
The Thunderbird page is no help, it offers me the download, but no instructions on how to install it over an existing installation. Do I just extract the directory? Maybe it will "just work". Maybe it will screw everything up.
Reading through the thread, I see posts here and there directing people to install repositories (e.g. for Firefox or Thunderbird). Perhaps the directions for adding repositories (and how to find out what those repositories are) could be added. (That's assuming adding the repositories is safe.)