Landed on comm-central, possible candidate for 2.42.x if continued on 45 ESR:
* {{Bug|1229270}} Provide UI in Send Format pane for new mailnews.sendformat.auto_downgrade preference.
Waiting for review:
* {{Bug|1237835}} Document IMAP IDLE setting which {{bug|449021}} moved to main account settings screen.
May need retargeting:
* {{Bug|1123673}} Consider exposing security.tls.version.fallback-limit in SSL prefpane to accommodate SSL 3.0 legacy sites.