Recently, uBlue. It’s more a family of fedora atomic images but it has taken the pain out of immutability for me. I was using Fedora silver blue and later Sericea a while back, but installing codecs from RPMfusion on it never worked properly and my hw acceleration was always broken. I was on NixOS for a while but had sporadic problems that come with NixOS not using an FHS structure. But uBlue just works. Hardware acceleration works out of the box, and I can easily create custom images with BlueBuild. It’s a very nice ecosystem to create a stable, secure, complete base system. And I run nix on top of it for user packages and home-manager to get all the benefits of both worlds
Mostly LibreWolf, but I’ve been enjoying Zen Browser recently. It’s based on Firefox but with lots of cool extra functionality baked in. It is still in alpha though and I’ve experienced some bugs, including it crashing my whole system a couple of times, but it’s very promising