This bug seems to be Fedora specific since I've tried nightly builds from mozilla.org and they work fine. The problem is that Thunderbird crashes rather often when you try and delete text in the compose window. Trying to delete quoted text (when replying) seems particularly error prone. Very annyoing since you have to keep saving your mail into draft constantly out of fear for the next imminent crash.
confirming that i've been experiencing this misbehavior as well.
Could you please install thunderbird-debuginfo and get a gdb backtrace? Does it match Bug #176201? If so, then this report is a duplicate.
seems to be the same. *** This bug has been marked as a duplicate of 176201 ***