To set a Firefox about:config entry programmatically using Selenium without modifying the file system profile or web-scraping about:config, you can use Firefox's preferences (also known as "prefs") system. Selenium allows you to set preferences directly when launching the browser via FirefoxOptions.

How to Set a about:config Entry via Selenium

1. Use FirefoxOptions to set preferences before launching the browser.
2. Map the about:config key to its corresponding preference name (e.g., browser.startup.homepage for the homepage).
3. Pass the preferences to the Firefox driver.

Example Code

from selenium import webdriver
from selenium.webdriver.firefox.options import Options

# Create Firefox options
options = Options()

# Set the preference (replace 'pref_name' and 'pref_value' with your target)
options.set_preference("pref_name", "pref_value")

# Example: Disable Firefox's default "new tab" page
options.set_preference("browser.newtabpage.enabled", False)

# Example: Set a custom homepage
options.set_preference("browser.startup.homepage", "https://example.com")

# Launch Firefox with the options
driver = webdriver.Firefox(options=options)

# Continue with your Selenium script
driver.get("https://example.com")

Key Notes

• Preference Names: The preference names in about:config are the same as those used in set_preference. For example:
  • browser.startup.homepage → Homepage URL
  • network.proxy.type → Proxy type (0 = direct, 1 = manual, etc.)
  • privacy.trackingprotection.enabled → Tracking protection
• Boolean/Integer/String: Use the appropriate Python type for the preference value (e.g., True/False for booleans, 1 for integers, "value" for strings).
• No File System Modifications: This method does not touch the filesystem or require scraping about:config.

How to Find the Correct Preference Name

1. Open about:config in Firefox.
2. Search for the setting you want to change.
3. The Name column is the preference name to use in set_preference.

Limitations

• Not all about:config entries can be set this way (e.g., some are read-only or require browser restarts).
• Some preferences may require a browser restart to take effect. In such cases, you may need to set them in the profile before launching Selenium.