I think most Firefox users on Hacker News would dispute this. Judging by the average thread on Firefox, most of us think that Mozilla's efforts have mostly been to make Firefox worse. I don't know that I'd go that far, but the issue seems to be that most of the user facing changes have been the kind of pointless changes for the sake of change, and side projects most people don't use or want in their browser.

A sibling comment mentions breaking the addon API. If the addons I want to use are broken for months at a time, that's going to get me to consider using a different browser, even one with less capabilities. (This doesn't have to be a rational process; ideally you want your users to never think "ugh, why isn't this working, hmm I haven't checked out Chrome in a while". Even if Chrome is worse, some of them are going to switch.)

Then there's Pocket, which (let's admit) exists only because it's a direct source of revenue for Mozilla via advertisements placed in the browser chrome.

Then there's the pointless change to the URL bar, which drew an absurd amount of outrage. That much anger over a small UI change is not justified of course, but that's not the point. Stuff like this breaks the cardinal rule of not pointlessly pissing off your dwindling user base.

There's whatever the hell the mobile team is up to, with some new perpetual beta project every 12 months and putting an enormous amount of effort into a new Firefox for Android with a worse, slower UI that's not significantly faster for actual browsing and currently only has support for a handful of addons (which are the only reason anyone uses FFA).

There's enhanced tracking protection, which in the good ol' days of Firefox would have been an addon. Granted, it seems like it's doing something genuinely useful.

The RSS viewer got removed in version 64.

Then there are the fiascos, like the time Mozilla broke all users' addons, the hotfix sideloading scandal, the Mr Robot thing...

To be clear I do recognize that at least some parts of Mozilla are interested in improving Firefox, but the issue is that most of the improvements there are not obvious to anyone. Personally I've enjoyed the feature to automatically block notification permission requests (the UI for that is great). The addition of WebP support was nice, and ongoing work to support AVIF is also appreciated. The work on WebRender and introducing Rust code into Firefox is appreciated and has made Firefox noticeably faster. There have been some nice improvements to the developer tools too.

The problem is that most of this stuff isn't visible to ordinary users, even to power users. That's a problem for attracting new users, to be sure. But the attempts Mozilla has made to attract new users seem to largely be failing. And so the worst thing they could possibly do is to piss off the dedicated users who remain, but that seems to be what they've mostly accomplished.