A recent update of Thunderbird in Ubuntu (version 60.2.1) broke the Lightning calendar installed as add-on. See here. Mozilla provides Lightning as bundled in the last versions, but Ubuntu (and Debian?) package do not, so now there is a mismatch between the Thunderbird version in the repositories and the add-on provided by Mozilla (5.4, only useful for Thunderbird 52).
One suggested option is to search and install beta releases provided by Mozilla, but it looks as a workaround (future automatic updates are compromised). Another is to delete the non-compatible Ligthning add-on and install a separate package (
xul-ext-lightning) via apt, but it is not localised (only available in English since at least 2010).
So, which is the proper "future-proof" way to install Lightning in Mozilla Thunderbird from now on (as intended by Ubuntu maintainers)?
- Remove the internal add-on (
.xpi) and install (
xul-ext-lightning) [this package will be updated accordingly, together with Thunderbird and, eventually, localised]
- Keep the Mozilla add-on until the mismatch with Thunderbird apt package is fixed
- Remove the add-on and wait until a future Thunderbird apt package provides it integrated (as Mozilla bundles it for other platforms)
xul-ext-lightninghas not been fixed for i18n in the last 10 years, i would not hold my breath.