lts,release-management – Difference Between Long Term Support Release and Normal Release

Because we use Firefox 11 instead of ESR and most of the same reasons apply to Thunderbird as Firefox for using the rapid release version. The decision to not use ESR by default in the LTS was surprising to me, so I asked on the mailinglists (you can find the thread here: https://lists.ubuntu.com/archives/ubuntu-desktop/2012-February/003672.html) and Jason Warner from Canonical answered:

Firefox adopted a rapid release model for various reasons, but among them was that they needed the browser to keep up with the pace of innovation on the internet. Ubuntu needs to be out in front of these things and be pushing the very edge of what is possible, particularly in the browser. I do not think we can ship a browser that will lag by 12 months in any sense; the risks too far outweigh the rewards.

I'm afraid that even a year lag (ESR update period) would put Ubuntu at severe disadvantage to other platforms. Imagine a world where G+ or Facebook or some new whizbang product didn't work on Ubuntu because the browser shipped didn't support some new technology/javascript engine/platform component. That is neither something we want nor can afford. We have to be better, we have to be faster and we have to be braver.

Anyway, you'd like to install Thunderbird ESR, you can donwload it here: http://mozilla.org/en-US/thunderbird/organizations/all-esr.html You simply need to extract it into your home folder and add a script called ~/bin/thunderbird to launch ~/thunderbird_folder/thunderbird $@ every time your user calls thunderbird

You can also see this blog post from Chris Coulson on why the ESR was not selected.

The Ubuntu Help site has the answer:

1. "Important Security Updates (raring-security)". Patches for security vulnerabilities in Ubuntu packages. They are managed by the Ubuntu Security Team and are designed to change the behavior of the package as little as possible -- in fact, the minimum required to resolve the security problem. As a result, they tend to be very low-risk to apply and all users are urged to apply security updates.
2. "Recommended Updates (raring-updates)". Updates for serious bugs in Ubuntu packaging that do not affect the security of the system.
3. "Pre-released Updates (raring-proposed)". The testing area for updates. This repository is recommended only to those interested in helping to test updates and provide feedback.
4. "Unsupported Updates (raring-backports)". As the name states, these are unsupported new versions of packages which have been backported to an older release. Packages may contain new features, may introduce new interfaces, and bugs.

For example, the phpldapadmin package that was released for trusty has a serious packaging bug, where it expected a directory structure use in Apache 2.2, whereas trusty had Apache 2.4. It couldn't even be installed. The fix was released in trusty-updates.

For most users, enabling all four shouldn't be a problem most of the time. For a very stable environment, keep only security enabled. Keep updates enabled if some package you're using has a packaging issue. Updates packages have to conform to policies regarding stable updates, so they shouldn't cause breakage and keeping them enabled all the time is recommended. Keep proposed enabled if you don't mind testing out new things. This might cause things to break on occasion, so if you're not a fan of the " latest and greatest" philosophy, keep it disabled unless you have a problem and devs ask you to enable it. Keep backports enabled if you wish to have software that is typically only available for a newer release of Ubuntu.