"about:config" - advanced preferences for Thunderbird: (configuration tested in version 2, related settings can be assumed to have default values)
Check all folders automatically instead of having to toggle "check mail" for each IMAP folder:
- mail.check_all_imap_folders_for_new = true
Display HTML e-mails as text:
- mailnews.display.html_as = 1
Don't thread e-mails based on subject line only, unless it has a <strong>Re:</strong> tag:
- mail.thread_without_re = false
Change default sorting order for new folders:
- mailnews.default_view_flags = 1 (threaded view, see Bugzilla
Possibly try this to avoid "hanging" on some large attachments: (this option is now present in the View menu, not sure since when)
- mail.inline_attachments = false
For those who have several e-mail addresses to choose from as a sender, you may want to check out the Correct Identity extension, which can do more sophisticated selections (controlled by rules that you line up) than Thunderbird itself can.
As a Swede, I prefer our own (actually standardized… ;-)) date format. See mozillaZine which helped me use sv_SE for time formatting and my system default (en_GB) for the rest.