IE9 should get back to basics
NO "pre defined" plugins, no stupid "Accelerators", etc etc.
The browser should just be a Browser -- no more and no less. That way it would be lightning fast.
Provide an API for any 3rd party plugins -- you'll kill 99% of viruses and nasties with this.
If people want to run scripts, adobe reader, multi media etc then this should be launched as a separate app -- not run from within the browser itself.