It appears that, IE requires some time to settle after the main UI is displayed. Launch ie9, the first tab (suddenly appears -comparable with any agile browser- but) gets frozen for a while and then regains consciousness (back to ready state - something to do with the main UI thread). If you immediately try entering a URL in the address bar, it would be reverted to the homepage URL once the browser is in ready state.
This behavior is observed after disabling all the add-ons on ie9. This behavior also exist in older versions ie8 & 7. Other browsers appear to have more fluid/organic UI specifically at application startup.