Rated 3 out of 5 stars
Echoing some comments of Gordon Lack: several buttons I'd used in TB2 did reappear on my toolbar after upgrading to TB3, but perform nothing (or nothing useful) any more.
It took me 3 days to find anything for navigating to the next or the previous message without leaving my current tab (seems basic and vital, no?). The old buttons had appeared but, in TB3, are duds. The *actually working* TB3 buttons for these functions (I just located minutes ago) look almost identical to the ones for finding the next/previous unread message - which I would never happen to need. I'm suggesting these two sets of buttons should look much more different from each other.