What about Safari's Webkit?
Yes, Webkit is another one. But Google's Blink is actually a fork of Webkit, they have some similarities. Besides, Safari is available on MacOS and iOS only so it's far less important. As we all know, Apple is also kind of stubborn and they like to do things their own away. So, Firefox is the only major competitor to Chromium I think.
Thanks for your opinion. Unfortunately, Firefox (and its many derivatives) has never grabbed a large portion of the market, and I doubt it ever will, so I can't consider it much of a competitor. The Chromium-based browsers seem to be much more popular. And fortunately, Chromium is open-source.
Firefox had a huge market share in the past then Chrome came with simple design and everyone loved it. It was nice and simple back then. One of the reason Chrome even got more popular is Android. Even now every Android phone comes with Chrome installed(which is about to change because of pressure from EU or something) and year by year it surpassed every browsers. But don't forget Google is an ad company, 85% of their revenue comes from ads and by using Chrome, users are letting google know what they do on the web. One of the reason Firefox fall behind is Firefox OS. You probably know few years ago Mozilla tried to create an OS, so back then they shifted their main focus from Firefox as a result Firefox fall behind of Chrome on adding new features.
BTW, Chromium is open source but Chrome isn't. If everyone switches to Chromium, it would give google the complete control over the web, there would be no open web standards. They'll do what they want to do to fulfill their needs. Take Google's AMP pages as an example. Almost no one wanted to use AMP pages at first. So, to force publishers, Google started to show AMP pages at the top of their search results so publishers were forced to have an AMP version of their pages so that they can appear on the first search result page. Manipulation of their power.
Currently Firefox is very good actually, as fast as Chrome except on most Google's sites. A Microsoft engineer said few months ago with proof that Google intentionally slows down YouTube on other browsers.
Even Google Earth, it's been two years I think Google released the new Google Earth web version and few months later they teased with a screenshot that Firefox support is coming soon, 1.5 years has passed since that announcement and still no news of Google Earth on Firefox.
There are many cases like this where Google does evil things.
That's why I support Firefox, a non-profit organization trying their best to fight against Google's monopoly.