I’m using librewolf. I’m not sure it’s on your end. I think something else might be going on.

Just a simple little nitpick:

On the Nix/NixOS section of install, you type

Alternatively, for non-NixOS users, you can spawn a temporary shell with Managarr available like so: nix-shell -p managarr

nix-shell -p managarr works just fine on NixOS proper. I use it all the time.

I get this when I click on the demo. Uh, I don’t know why.