How to Bookmark website without informing user(visitor) of website?
And How to set as browsers homepage without informing user?

You can bring up the dialog box asking the user "Would you like to bookmark this page?" but, as far as I know, you can't do anything without there intervention and approval. Regardless, anything you would do would be done through Javascript, not PHP.

ok,
I have seen (that irritating)babylon dictionary toolbar, when it comes, it changes browser homepage without asking user.