In bug 457941 I suggested that maybe the first of the rsync commands in browser/app/Makefile.in should use --delete, so that we don't leave old stuff in Firefox.app that causes problems in depend builds that don't happen in a build from a fresh tree. I wanted to file a bug on this before I forgot about it. This is in some ways similar to bug 455940... and the underlying problem might be fixed by a patch there.
Mass bug cleanup for Core:Build Config. If you feel this bug has been closed in error, please re-open with new details.