Looks like it was a straggler that never got converted. Fix is to add nsIFactory.idl to XPIDLSRCS in the Makefile.in and makefile.win, and add the appropriate Mac project for the .xpt files.
Marking as assigned. Also nsIProxyCreateInstance.h, nsINNTPNewsgroupPost.h I just found these because they had the antiquated XPIDL_JS_STUBS #ifdefs; it would also be fruitful to look for others in the tree. (Keyed off of the GENERATED FILE comment.)
should replace method declarations in implementations with NS_DECL_NSIFACTORY when nsIFactory.h is generated.
It seems to have gone away.
Not present according to LXR, 6pm 20010522