From MozillaZine Knowledge Base

I was going to number the items (in the list of things to try) but decided not to. That way, if someone adds a new item to the middle of the list, the whole list won't need to be renumbered. Wintogreen 07:19, 24 Mar 2004 (PST)

I agree with your reasoning.

My suggestion is to emphasize that it is necessary to set the "View > Messages > All" (or recent, etc)for each folder My problem was trying to view sent messages and the setting was for unread messages so the screen came up blank. 

Jonathan Milne-fowler 12:40 UCT 27 June 2005.

i am facing another kind of problem for disappering mails from Inbox. I was downloading mails thru Thunderbird when due to Power Failure my PC was switched off. When I turned on the PC and started Thunderbird all mails in Inbox have disappered whereas the Total mails in the status bar at bottom shows that there are 10 mails in the Inbox. Plz suggest the solution for it.