Thunderbird : Tips

General tips

Check out the keyboard shortcuts for Thunderbird.
Change the keybindings with the Keyconfig extension.
Launch Thunderbird using command line options (list is for the Mozilla Suite; not all options work with Thunderbird).
Read these tips for using antivirus software with Thunderbird.
Make regular backups of your email messages, address books, and account settings.
For best performance, compact folders periodically.
When something's amiss, try creating a new profile.

Try a new theme to give Thunderbird a different look.
Customize the toolbar: add/remove buttons, change the placement of buttons, etc.
Arrange the columns in the message-list pane.
Show expanded columns in the folders pane for number of unread messages, total, or size.
Change the order of accounts in the folders pane.
Change the fonts used in the folders pane, message-list pane, and menus.
Change the background color in the preview pane and other panes.
Change the color of links in messages or turn off the underlining of links.
Change the signature display color (so that everything below "-- " isn't gray).
Change the menu highlight color (by inserting code into your userChrome.css file).
Get rid of the colored quote bars and use ">" instead.
Change the display format for date and time for messages from today, the past week, or all previous dates.
Adjust the height of the attachments pane and add a scrollbar to it.

Try new extensions to give added functionality to Thunderbird; you'll be surprised.
Uninstalling extensions
Safe Mode: use this to start up Thunderbird with all your extensions disabled (useful for debugging)

More great tips are available at mozilla.org's Thunderbird Help: Tips & Tricks page.