It's internal. They are becoming irrelevant (their browser market share have been shrinking for years now), so they are jumping all the new hype trends now. They literally just became an ad company. We have Google, Apple, Brave and Mozilla all being an ad companies that produce browsers.
There is also Vivaldi (based on Chromium/Blink) which is employee owned, but the choices are shrinking.
Mozilla Foundation is still non-profit, but Mozilla Corporation is not. And while they claim to operate by Mozilla Manifesto, it's non-binding and has been broken multiple times. Remember Pocket and their promise to open source it?
Microsoft dominated with IE back in the day for the same reason Chrome and Safari are the dominant choices. People don't tend to change the default if it works okay enough. Firefox dropped heavily years ago as the market was saturated with other new choices already installed on mobile and Chromebooks, but recent numbers are about the same as they have been for a while. Maybe even still growing, as all the numbers I find are percentages, and there's no doubt we've had an explosion of device use.