Automatically click the button on a page that is not mine

Is it possible to automatically click on a button that exists on any page?
I’m talking about a page that I’m not creating. It’s any page I find on the web.
I need a button on this page to be automatically clicked.
It’s possible?

Ish. There are extensions to the browser, things like greaseMonkey, which you could use to write a custom script to automatically click buttons.

Thank you snowmonkey,
is it possible to inject javascript without extensions?
I need to have a page 1 with the code to inject on page 2 and see the result.
Can you help me?