After the update Sept 19 2013 I have a problem with Thunderbird. I run Ubuntu 12.04.3 LTS and I use lubuntu-desktop most of the time.
The window to write letters (or reply to letters) is borked. There is no cursor, and although it is focused, the active window is still the main Thunderbird window, so I can't write anything. This happens after running Thunderbird for a while, and I had to close and re-open Thunderbird to be able to write a letter again.
Now I have found that it is simpler and also more successful to close the main window of Thunderbird. Then the cursor will appear in the 'Write' window, and I can write the letter or reply/forward the letter as intended.
I have seen a similar problem in my other mozilla application, Firefox, if I have two windows open. I can live with the Firefox problem, but I mention it, because it is similar, and it could be caused by the same bug. This problem in Firefox has been there for months, but the problem in Thunderbird is new, it started Sept 19 2013.
What can I do to fix it? I hope I need not start all over with a fresh install of Thunderbird.
If you have the same or a similar problem, please click 'This bug affects you' at the Launchpad bug report