I found a workaround. A backtrace in gdb showed, that libflashplayer has something to do with the crashes. After uninstalling Flashplayer, I can write emails again. Maybe it is already enough to deactivate the plugin /add-ons. I attach the backtrace.
** Attachment added: "backtrace.txt" https://bugs.launchpad.net/ubuntu/+source/thunderbird/+bug/1315289/+attachment/4103165/+files/backtrace.txt -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1315289 Title: Thunderbird 24.5.0 on Ubuntu 13.10 crashes when opening a new mail To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/thunderbird/+bug/1315289/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs