With the experimental “Compose in a tab” extension, you can now (partly) do in Thunderbird what you could do in Outlook for most of the 2000s – WYSIWYG editing (by using CKEditor). Although creating tables – my one big wish – is still nowhere up to the mark.
Also, with the Contacts for Thunderbird extension, you can now auto-complete contacts in the Thunderbird message compose window by pulling data from a number of sources – your local address book, Gmail, Linkedin and more – but not, tragically, from LDAP yet. I really want to love Thunderbird but can’t – I return to Outlook. Just like I really want to love Firefox, but Chrome’s just better.