On the Thunderbird tinderboxes, we have been doing optimized, no debug, dep builds and running "make check" on just the mailnews/ directory. Several times we have seen a change that affects either the mailnews idl files, or in one case just the object file, cause an orange on the tinderboxes. A follow-on build (where nothing changes) fixes it. I have reproduced this locally: 1) Build Thunderbird 2) make -C mailnews check (passes) 3) Apply (or remove a patch) e.g. bug 413260/bug 449618 where ones we had problems on. 4) Rebuild Thunderbird (dep build) 5) make -C mailnews check This last step fails. On bug 449618 it was causing segfaults. When we checked in bug 413260 it was one of the NS_ERROR_XPC_* error codes (http://mxr.mozilla.org/comm-central/source/mozilla/js/src/xpconnect/idl/nsIXPConnect.idl) The following alternatives for stage 5 would make the tests pass: a) running "make check" twice, ignoring the first search results b) running the full "make check" (including core etc) with a patched set of tests, to avoid the ones that currently fail (which is currently blocked by bug 431125). So my guess is that xpcshell is not always picking up changes in registrations/library too well. Apart from that I'm not sure what would help.

I don't think we've seen this recently, so closing.