"better" is completely subjective. From my point of view dev tools are way better in Blink-based browsers, so Chrome is my default dev browser. The browsing experience is really good in Safari, I love the compact tabs and minimalist UI, so that's my default on macOS. Edge has a really nice productivity feature that lets you split a window to see two different pages at the same time, so that's my default on Windows. Other than being open source I don't see what would compel me to go back to Firefox in 2024, the competition improved a lot. Also I personally lost faith in the Mozilla Foundation.
I've been using Firefox for about as long as I can remember, and really don't notice sites not working. I do notice, however, that using any browser without UBO makes my eyes bleed in an unending agony of capitalist garbage. It's like using a browser and then putting sand in your eyeballs.
That is quite literally Firefox + UBO. Like it's literally a fork of the tor browser (which is downstream firefox) with a custom config and preconfigured addons.
I don't mean this as a dig or anything but it's literally what they described.
Yes for the GP but UBO on firefox isn't defaults either. The bulk of the benefits you get from mullvad browser past what you get with default firefox + the same extensions are easy config changes. Things you can accomplish by just scrolling through the settings and flipping on a few settings with "more secure more better" worded descriptions.
For the average user there's not really a particularly good reason to jump for a downstream browser unless you are specifically using their main features (tor or VPN). It's easy enough to get 95% of the way there with 30 seconds of config tweaks off stock upstream.
The mullvad browser defaults would get it chucked in the bin very quickly by the average web user.
The extreme bent towards privacy and not retaining any identifiable or fingerprint-able behaviors is exactly what its target audience wants, of course. But it leads to a markedly more inconvenient experience than Chrome or default Firefox or Safari.