Not automatically, at least not with all browsers. I made [this add-on]
(https://vaadin.com/directory/component/fullscreen/overview) to toggle fullscreen mode, and in doing so, I discovered that at least some browsers require the fullscreen mode to be toggled from a user action, so in the add-on’s case it’s done with a button click. The browser will ignore the JavaScript call if you’re trying to execute it without user interaction.