In Firefox, stylesheets will block all other downloads. This is especially bad for external scripts, because stylesheets and external scripts are frequently placed near each other in the page. This page contains a stylesheet (2 second download), an external script (1 second download, 1 second execution), and an image (2 second download). As shown in the Firefox HTTP profile below, all of these items load sequentially making the total page load in a little over 6 seconds. Notice the white gap after the script and before the image; this is the 1 second script execution time.