Not an attack on open source
"But Morris said that the idea of starting with open source didn't last long in Redmond because Microsoft wanted to control its own code."
He didn't say that at all, not at all. That's just your spin on what he really said, which is the need for speed of delivering an interoperable engine faster, as he said in the very next sentence of your post:
"Given the engineering effort required, we found that we could deliver an interoperability focused engine to customers significantly faster if we started from our own engine (especially if unshackled from legacy compatibility concerns), rather than building up a new browser around an open-source engine.,"