Firejail requires SUID, LandLock does not.

Also, it's very easy to write your own LandLock policy in the programming language of your choice and wrap whatever program you like rather than downloading stuff from Github. Here's another example in Go:

    package main

    import (
     "fmt"
     "github.com/landlock-lsm/go-landlock/landlock"
     "log"
     "os"
     "os/exec"
    )

    func main() {
        // Define the LandLock policy
        err := landlock.V1.RestrictPaths(...)

        // Execute FireFox
        cmd := exec.Command("/usr/bin/firefox")
    }