To make things clear, everything was fine at the end of the day before yesterday. At that time, I was using Seamonkey2.3.3 and Thunderbird 6.0.2. No new addon had been installed in days. Seamonkey was my default for browser and mail. Yesterday morning I noticed the first problems with Seamonkey, still the same version. Either in mail or in browser, it started hanging, after doing a single operation. In other words, I could read one page or e-mail, but not a second one. I upgraded Seamonkey to 2.4, with no change in behavior. Then, I checked Firefox, and it was working fine, but Thunderbird was, also, hanging.
I tried the following:
1. uninstall of Seamonkey, followed by clean install
2. Starting in Safe Mode (addons disabled).
Typically, I could delete messages, and dump the Trash, but compacting did not work, partially, or at all.
One particular message, sent by my son with 37 images, kept coming in, but had small size, and fewer pictures.
One e-mail could not be deleted. And, another smaller e-mail kept coming in, every time I opened the program.
I did virus and malware scans. Nothing looked awry.
The original profile contained two places.sqlite.corrupt files, which I deleted.
Mail looks fine in Outlook Express.
As for Firefox, the normal FF7 seems ok, but it does not login this site (I never logoff), and FF7 portable has no scroll band.
And, why not, there is a Thunderbird 7, paralleling Firefox 7, but I have not tried it.