Most browsers today are open source versions based on Chromium, Google Chrome, but a few choose another open source browser, Firefox, one of which is Cliqz. Cliqz, which launched its own desktop browser based on Firefox in 2015, posted a blog post explaining why it created branches on Firefox instead of Chromium:
Technically speaking, all of Firefox’s browser features have an open API, while Chromium retains a sensitive place for Google’s business, a typical example is the address bar, which Google has no intention of making it easier for others to control the address bar, and the flow of the default search engine is protected, creating New APIs can solve these problems, but maintaining them is another challenge.
Google’s support for older APIs is neither consistent nor consistent, and Chrome’s new API, Manifest v3, replaces the old, more powerful and useful APIs for privacy, security, and performance reasons.
Chrome’s bundled Google services are also not easy to remove, and Microsoft and Brave have invested heavily in divesting them.