When you invoke get() for an url using Selenium a lot many actions happens under the hood, including HTTP requests received by geckodriver, packets sent to and from the remote protocol in Firefox, and responses sent back to your client.

Once the basic mandatory requests/responses are successfully completed, based on the pageLoadStrategy the browser i.e. the client sends back the program control to Selenium to perform the next line of code.

Now pageLoadStrategy can be either of the following:

• normail: This stategy causes Selenium to wait for the full page loading (html content and subresources downloaded and parsed).
• eager: This stategy causes Selenium to wait for the DOMContentLoaded event (html content downloaded and parsed only).
• none: This strategy causes Selenium to return immediately after the initial page content is fully received (html content downloaded).

So once the program control is returned back to Selenium based on pageLoadStrategy which is somewhat timebound, then only driver.quit() can be performed.