If you have a setTimeout() call that runs inline during the _first_ document load (in viewer only), it silently fails here: http://lxr.mozilla.org/seamonkey/source/dom/src/base/nsGlobalWindow.cpp#1819 because it can't get the document's principal. This scares me, because it makes me wonder if we have an off-by-one case where the timeout is always using the last principal.
I'd already reworked GlobalWindowImpl::GetPrincipal as part of some other work I've been doing. With my existing changes, the problem doesn't appear. My changes affect over thirty files, so getting them into the tree will take a little effort. I'll try to do it by Monday.
Fixed with 8/29 checkin
Moving all CAPS bugs to Security: CAPS component. CAPS component will be deleted.