With the 19.0 cycle now released, scheduled support for the 10.0 ESR branch should end, thus 10.0.12 ESR is likely the final release on that branch.
I'm not sure if there will be a major update offered for 10.0 ESR users to upgrade to the current 17.0 ESR release, but you can always download the installer following the link above and just run it over your current 10.0 ESR installation.
Noticeable changes and adjustments you may consider to apply prior to deployment of this update:
- The 17.0 release features a new chat component. It can't be uninstalled, but deactivated by setting the mail.chat.enabled preference to "false" (if you don't want people to use chat).
- Similarly, large attachments can be stored with on-line ("cloud") services. To deactivate this feature, set mail.cloud_files.enabled to "false".
- The TestPilot extension installs itself, allowing users to participate in any Mozilla-initiated usage studies. Remove distribution/extensions/tbtestpilot@labs.mozilla.com.xpi from the installation directory prior to deployment to avoid that, or use the Add-ons Manager to remove it after the installation.
- At least on Windows, the title bar may not be visible if Thunderbird is allowed to draw into it. The regular window decoration can be enabled by setting mail.tabs.drawInTitlebar to "false".
- It may be a matter of taste whether to use the traditional menus or the new Application Button (≡) for navigation, but you can enable the old menus by typing Alt+V to make the "View" menu visible, then "Toolbars" and tick "Menu bar" to make it stick.
- "Tabs on top" is enforced with 17.0, no configuration option but an extension is available to move the toolbar back above the tabs.