Thanks for the suggestion but that does not work for the volume and variety of emails that I need to see real time. The ONLY change to my system has been the updates to Firefox, so something has changed within that application. Furthermore, all mouse and drag and drop functions work as they always have in all other applications.

Firefox updates don't touch Thunderbird files, they are two separate programs. You do need to update Thunderbird however, please update to 24.3.0, it contains the latest security and stability fixes and we can't help you using the older version.

Actually, it looks like you are running Mac 10.5, so you won't be able to update thunderbird. You should seriously consider updating to Mac 10.6 or later asap.

Sorry for the confusion, I meant to say Thunderbird in the previous post. Yes, I am on a Mac running 10.5.8 with both Firefox and Thunderbird at 16.0.2.