I also use Niagara Launcher. I know it’s not FOSS, but non of these have the mix of effortlessness and functions like Niagara.

Zen Browers gives a new look and feel to Firefox, while Floorp uses the same design and makes their added features look like some extenstions rather then build in features.

And I think a big advantage for Zen browser is, that it presents itself as an OSS alternative for the popular Arc browser, without mandatory account.