WebKit and Chromium are hard forks. The former is a fork of KHTML, and the latter is a hard fork of the former. However, in recent years I’ve only seen soft forks, and as for hard forks, I’ve only seen one with Pale Moon, which hard forked Gecko and named it Goanna due to disagreements with the direction the Mozilla Project was taking.
But why wouldn’t any organization make a hard fork, whether of WebKit, Chromium, Firefox, or another browser not based on the three mentioned above?
What a lot of people are forgetting to mention here, is that the reason why maintaining a browser is so hard is because Google keeps updating the standards, and has the resources to do so, while Firefox struggles to keep up.
Remember, Google Chrome is Google’s OS. Like Microsoft has Windows, and Apple has MacOS. This is why web standards include support for USB, GPU, and other esoteric use cases. It’s in Google’s best interest for users to use web apps to do things instead of desktop apps, since that means they are likely using Chrome, within Google’s control. And Google has a perverse incentive to keep evolving these standards so that other browsers struggle to keep up, and their browsers feel outdated and feature lacking relative to Chrome.
ditto with their office software and filesystems.