Major
4.0.0
Major version. Check its notes for changes you have to act on before you upgrade.
With this version, we're using geckodriver to control Firefox. This means that you need to run Firefox v50 or newer. The main rationale for making the switch is that we now can screenshot only the rendered component. Previously, we've been screenshotting the entire page, then cropping to only include the component. Pre-cropped screenshots bring a significant performance improvement.