nm libxul.so |grep ' T '|wc gives me 59392 entries text section(which are usually code), The log produced with this patch reports 30444 libxul functions ran. Since it's just over 50% of the file that would be paged in on startup. I think doing readahead on it is completely reasonable.

Note that the above patch produces numbers that dlsym typically fails to resolve, so if one wanted to get better names, it's best to see what nsTraceRefcntImpl::WalkTheStack does