The following code disables stylesheets and images on a page loaded with Selenium Firefox webdriver:
from selenium import webdriver
firefox_profile = webdriver.
The google logo come form the css, where the pictures are embedded in the HTML as data (img src="data:image/jpeg;base64, ....) the code disable the loading of remote images not this type of sources
permissions.default.stylesheet: disable any formatting
permissions.default.image: disable any image and css background-image
if the image is embedded into the page as base64 encoded is not blocked by these permissions because is part of the HTML code (see http://en.wikipedia.org/wiki/Data_URI_scheme)
to disable more formatting you should add: