To run Selenium in an already open browser window

 To run Selenium in an already open browser window, you need to use the `attachToSession` method of the `RemoteWebDriver` class. This method allows you to attach your Selenium script to an existing browser session, instead of launching a new browser instance. 

Here is an example code in Python that shows how to attach to an already open Chrome window:

```python

from selenium import webdriver

# get the session ID of the open Chrome window

chrome_session_id = input("Please enter the session ID of the open Chrome window: ")

# attach to the session using RemoteWebDriver

chrome_options = webdriver.ChromeOptions()

chrome_options.add_argument("--start-maximized")

driver = webdriver.Remote(command_executor="http://localhost:9515", options=chrome_options)

driver.session_id = chrome_session_id

# navigate to a URL using the attached Chrome window

driver.get("https://www.google.com")

```

In this code, the `input` function prompts the user to enter the session ID of the open Chrome window. You can obtain the session ID by running the command `chrome://version/` in the address bar of the open Chrome window and looking for the value of the `Remote debugging port` field.

After obtaining the session ID, the code creates a `RemoteWebDriver` object and attaches it to the open Chrome window using the `session_id` property. Finally, the script navigates to a URL using the attached Chrome window.