Honestly Google did everything they could to help FF (to the tune of $400M/year) and Mozilla squandered it. Really sad.
Edit: Before this comment gets downvoted I want to try to explain it. When Brendan Eich wanted to make a new browser, he could've based it on Firefox/Gecko, which he had decades of experience with, but he didn't. What a vote of no confidence. Then Rust was invented because they thought creating a new language was the best way to catch up to Chrome's security. Even if you like Rust, you have to admit that was a bad decision for Mozilla's management.
Mozilla was the good guys, but being the good guys doesn't automatically mean you'll win. Too much wishful thinking can easily cloud one's judgment.
I'm only writing this because I care.
That most certainly had nothing to do with the large advertisement on the Google-owned most visited web page in the world and the way Google artificially limited their products on competing browser.
Please, look away regulators. Nothing to see here.
Edit: I have even forgotten to mention his they forced manufacturers to preinstall Chrome on every Android phones, an action for which they were fined 4.4 billions by the EU. Clearly the idea that Chrome won on technical merits need to die. Chrome market share was made through aggressive marketing and leveraging position in adjacent markets where Google is dominant.