You are asking something that is impossible. Please read this thread dating from December 2011. You'll find a snippet where Leonard Rosenthol, Adobe's PDF architect says: "there is no way to hide the toolbar (or the HUD) in the browser."
Setting the toolbar to false works for the toolbar, but you are referring to the "Heads Up Display" (HUD). As documented by Adobe, there is no way to customize this feature, let me quote Adobe:
the "Heads Up Display" (HUD) is not customizable. There are no APIs to HUD. You can’t use JavaScript to enter Read Mode, exit Read Mode or detect that the document is in Read Mode. Though it might seem like it, this wasn’t an oversight. There are some very sound engineering reasons why this is the case but I won’t go into those here.