Ever since Mozilla more or less put their email client on the sidetrack, it’s been pretty quiet about the Thunderbird. If anything, there was rather bad news about the stalled development, the old-fashioned design and dragged bugs. This might change with the long-awaited version jump from Thunderbird 52 to 60. This is literally “breaking” news, because the software was changed profoundly, so that many extensions didn’t work any more – a similar situation already existed with the major update of the Firefox browser.
Behind this is a platform change: Support for the old XUL extensions is switched off; instead Thunderbird now also uses the WebExtensions APIs. This means: many popular extensions won’t work anymore – unless a developer ports them to the new standard. See the website Thunderbird extensions to see the status of an individual extension. For the time being, the deactivation of XUL can still be levered out via a software switch – see the Ubuntalog entry for Thunderbird.
The break between Thunderbird 52 and 60 was big enough, that the developers initially deactivated the automatic upgrade – and thus even accepted that several errors classified as critical were not fixed. Thunderbird 60 was released on August 6, 2018, but users of the old version were not offered an upgrade until October 2, 2018, when Thunderbird 60.2.1 came out.