WetGeek I've installed and configured Thunderbird and Vivaldi on them, to make them more realistic installations.
That's my next step here, too. Since I don't yet know what package manager KaOS uses (it's independent, like Solus), I'll start out by using Octopi, the KaOS version of a software center.
I'll see if Vivaldi is available, since the provided browser is Falcon, apparently a KDE product. It accepts extensions from the KDE Store, but LastPass is not among them. That's a showstopper for me. I'll hold off on installing Thunderbird, since I can use Vivaldi for email, and I'll be installing that anyway (if I can).