I compared your strace with mine and there are several "file not found" in both but in yours there is
I havestat64("/usr/bin/run-mozilla.sh", 0xbfe62c3c) = -1 ENOENT (No such file or directory)
This is /usr/libstat64("../lib/thunderbird/run-mozilla.sh", {st_mode=S_IFREG|0755, st_size=10492, ...}) = 0