Mozilla did nothing to stop it and they were themselves ahead at one point. They were laughing all the way to the bank with Google and years later, Mozilla was thrown under the bus and sabotaged by Google and Chrome became the dominant browser. Now Mozilla is on life support.
How could Mozilla be so naive to sit on Google's money to let them propose for DRM standards, privacy violating APIs and suffocate Firefox into irrelevance? Mozilla did that to themselves for years and now they are crying.
Today, Firefox has become extremely irrelevant and totally overtaken by the Chromium derivatives and Safari. The best part is that the users do not care and companies like Snap will favour the most used browser and that is Chrome.
That there is the hard fact of the matter and the web just went from one behemoth (Microsoft) to another (Google). As long as those companies are sitting on the W3C dictating the direction of these web standards, the so called 'open web' is a myth.