- mailnews.default_view_flags: 0=unthreaded / 1=threaded
- mailnews.default_sort_type: 18=sort by date
- mailnews.default_sort_order: 1=ascending / 2=descending
Here's a copy of a post on "Sort order for mail/news not configurable by default (back-end part) thead on bugzilla" with the available configuration values:
Prefs are named as follows; first three apply to Mail and RSS folders, the second three to Newsgroups.
In about:config (Tools | Options | Advanced | General, Config Editor), you can enter "news._def" to filter out all the prefs but these.
byNone 17 byPriority 23 byLocation 29
byDate 18 * byStatus 24 byTags 30
bySubject 19 * bySize 25 byJunkStatus 31
byAuthor 20 * byFlagged 26 byAttachments 32
byId 21 ** byUnread 27 byAccount 33
byThread 22 byRecipient 28 byCustom 34
* = commonly desired values
** = by Order Received (?)
view_flags -- the second group of values can be added to one of the first group to combine effects, with several limitations:
Grouped 64 [mail only (?)]
ShowIgnored 8 [news only]
ShowExpanded 32 [doesn't seem to work]
ShowUnreadOnly will check the View|Threads|Unread menu; this will cause only
unread items to be seen, but doesn't force a threaded view.
Sort order for mail/news not configurable by default (back-end part)