Problem with start render time

[pmeenan]

The browser's parser stops for every non-async JS it encounters, waits for it to download, and then executes the script before it can proceed to the next bit of html. If any of those scripts use document.write() to inject other scripts then it needs to wait for those to download and execute before continuing.

This is by-spec and all browsers do it.

If css is pending then browsers will also not paint anything until the css finishes loading because that is what defines the layout of the content to paint.