Firefox users have often complained about the lack of substantial performance updates in the last few years, along with the divisive Firefox 89 UI overhaul that convinced some long-time users to try their luck with other browsers. It also doesn't help that Google Chrome is now the default browser on nearly all Android devices around the world, Microsoft Edge is doing the same on Windows machines, and we can't forget Safari on Macs and iPhones.
With more and more websites optimizing for Chrome so that they will load faster, it'll be an uphill battle for Firefox to remain competitive and peel users away from the Google ecosystem. With 197 million users, Firefox isn't going to disappear overnight, and some folks still really like what Mozilla is doing.