Today we shipped the last version in this year's beta program, Betterbird 153.0b9-bb5. We only shipped five beta versions, while the Thunderbird folks shipped nine versions, some with little or no relevant content, for example their releases revolving around there Thundermail system add-on which is disabled via a preference in Betterbird.
Next week we will ship Betterbird 153 ESR, first for Windows and in due course for Linux and Mac. We'll see how stable this series turns out to be and when we will start promoting it as the new primary version superseding version 140.
True to our motto
Betterbird is better than Thunderbird in three ways: It contains new features exclusive to Betterbird, it contains bug fixes exclusive to Betterbird and it contains fixes that Thunderbird may ship at a later stage
we are currently shipping 26 27 fixes the Thunderbird release team hasn't included in the 153 series, and which are only available on the Daily (alpha) channel, and months down the track, also on Thunderbird's regression-ridden release channel.
These 26 27 fixes include interesting new functionality, like the ability to store message (.eml) attachments directly in a folder, close to tray, Quick Look preview of attachments on Mac, various functional fixes, and also fixes for five more or less rare crashes.
Update: The Thunderbird folks decided to spin another beta, 153.0 beta 10, just to include one more fix, so Betterbird is now only 26 fixes ahead.