SeaMonkey 2.24 Beta 1

* Features
- The DoNotTrack and Prompt on Sanitize preferences are now kept in sync
- A pref (mailnews.p7m_external) has been added to allow users to choose an alternate application/pkcs7-mime handling
- Support for Atom Threading Extensions (RFC 4685) has been added
- Migrating profiles from Thunderbird supports the new signons file format now (support for the old format has been dropped)
- Autocomplete drop-downs (e.g. used on the Location Bar and Open Location dialog) now show favicons for their entries
- The account name is now displayed in the status bar for all messages when checking mail
- IMAP alert messages now show the server of the corresponding mail account
- Newsgroup names are now searched for all search strings combined (AND-search) on the subscribe dialog
* Fixes
- The return receipt request prompt had stopped appearing
- The value of the "Messages more than x days old" checkbox in Synchronization settings of News accounts is now saved correctly
- The MailNews context menu showed all possible options when only feed accounts were set up
- The Account Manager can be used again even if Local Directory is deemed unsafe
- The <items> list of feeds is now ignored, fixing the output of "(no subject)" articles while parsing the RSS of Planet Python
- Interfering with the restoring of a tab session could lead to an incomplete session getting saved
- HTML + plain-text (multipart) email messages with wrong encoding are now upgraded to UTF-8 properly
- The Folder Properties labels for incoming mail character encoding have been changed from "Default" to "Fallback"
- Help has been updated for the changes to SSL warnings and new options for the mixed content blocker on the SSL Preference pane
- Default Character Encoding has been renamed to Fallback Character Encoding (together with a note) on the Mail & Newsgroups Character Encoding Preferences pane
- The S/MIME Content-Description mail header could be invalid due to non-encoded 8-bit data
- Non-email feed author values were put in angle brackets, which could cause display issues in certain cases