rpm -qplv thunderbird-debuginfo-12.0.1-2.fc18.x86_64.rpm | grep libxul.so.debug
lrwxrwxrwx    1 root    root                       64 May  7 09:38 /usr/lib/debug/.build-id/ec/2eac414eb00d547f953d141170019222f76b11.1.debug -> ../../usr/lib64/thunderbird-devel-12.0.1/sdk/lib/libxul.so.debug
lrwxrwxrwx    1 root    root                       43 May  7 09:37 /usr/lib/debug/.build-id/ec/2eac414eb00d547f953d141170019222f76b11.debug -> ../../usr/lib64/thunderbird/libxul.so.debug
-r--r--r--    1 root    root                510144032 May  7 09:38 /usr/lib/debug/usr/lib64/thunderbird-devel-12.0.1/sdk/lib/libxul.so.debug
-r--r--r--    1 root    root                510144032 May  7 09:37 /usr/lib/debug/usr/lib64/thunderbird/libxul.so.debug

Note the huge .5GB files, which according to build-id and file size are most likely identical, but they aren't hardlinked.  Seen in F17 and F18.
I couldn't find where the thunderbird-devel-* libraries are actually shipped, so either you should be able to remove that directory before find-debuginfo.sh is run, or at least hardlink them together.  There are a few small *.debug files alongside of these, but as they are small they aren't as important.

Discovered while testing dwz utility and wondering why it needed so much memory on this package - the two .5GB identical files not hardlinked together result in
attempt of sharing most of the DIEs in it in a common file.