Closing this bug: somehow the global-messages-db.sqlite got confused, most likely because of a spam email that contained exactly 5000(!) recipients. Removing the global-messages-db.sqlite and global-messages- db.sqlite-journal files solved the problem.
** Changed in: thunderbird (Ubuntu) Status: New => Invalid -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1051175 Title: thunderbird increases memory from startup until whole system freezes because of lack of memory To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/thunderbird/+bug/1051175/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs