Hi - well just got around to uploading the dns lookup probes I was talking about. As always they are at bugzilla [#370906]. Changed my theme today as the font on the old one was driving me nuts 
I wanted to make a few changes.
When the dns lookup fires some where going to the cache and some to the network. It was a little confusing to see dnslookup-start probes firing without a matching dnslookup-done, which happened when you hit the cache. So I've added a dnslookup-init which is called for all initiated dnslookups, but only dnslookup-start and dnslookup-done get called when you go out on the net for the lookup.
I made similar changes to the load probes for the image loads. The load-init is called for all image requests, but only load-start and load-done are called when you go out on the net to fetch them.
The new load and dnslookup probes are:
Probes:
mozilla<pid>:::load-init
mozilla<pid>:::load-start
mozilla<pid>:::load-done
Args:
arg0 is of type void * - unique_id
arg1 is an enum nsTraceLoadType - TYPE_URI or TYPE_IMAGE
arg2 is of type struct nsTraceLoadInfo * - pointer to the URI info
mozilla<pid>:::dnslookup-init
mozilla<pid>:::dnslookup-start
mozilla<pid>:::dnslookup-done
Args:
arg0 is of type void * - unique_id
arg1 is of type struct nsTraceDNSLookupInfo * - pointer to the DNS lookup info
I've uploaded a new script which works with these new probes, along with some sample output. We still have the mystery of the 10 sec dns lookups, but hopefully we can figure that one out down the line, with a bit of help from the mozilla engineers, biesi if you have any ideas what's going on I'd really appreciate the dig out Is it some internal dnslookup thread pool issue?
Anyway I'm off traveling next week, but hope to get stuck into the other page load and dynamic update stages when I get back, including parsing, DOM construction, layout and paint. Lots of fun