Bug 944537 - No need to store showProgress as a Tab state/param (r=mfinkle)
Bug 944537 - Use message data to decide whether to show Tab progress or not (r=mfinkle)
Bug 944537 - No need to check for showProgress in BrowserToolbar (r=mfinkle)
Bug 944537 - Don't send showMessage boolean with Tabs.START event (r=mfinkle)