Problem: Inbox always appears empty on startup!
When I installed P-TBird, I neglected to disable "automatic updates". A week or so ago T-Bird 1.5.0.5 was auto installed on top of P-Tbird. This may or may not be related to my problem.
About the same time, everything left in my inbox from a previous session would be gone when I started the program. I searched Mozilla archives and discovered that this problem can happen if:
1. Too much mail is left in the inbox
2. Sub-directories of the inbox are created
One can test for this problem by doing a "Compact Files". I did so and all the missing messages re-appeared but were invisible again when I re-started. "Compact Files" would always bring them back.