You can install this (and indeed, many things) as a webapp, specifically a "PWA" aka "Progressive Web App". External reading:
Read on for quick-use tips and some snark.
On Android (and I think also iOS), simply tap ⋮ and then choose Add to Home Screen. It should give you an option to Install. Et voila!
On desktop OSes (Debian, Windows, MacOS, etc) the same should work, or there's a little install icon in the right side of the URL bar.
It should work on Android and iOS.
Despite Mozilla having once had an entire OS based on webapps, for years Firefox has required a third-party extension on the desktop. However, if you run Windows, support has finally returned as of September 2025. Linux and Mac users, Mozilla apparently doesn't really care about.
While not as fully-featured for normal browsing as Falkon, KDE's mobile-focused browser Angelfish has the option "Add to application launcher" which should work on at least KDE or compatible mobile and desktop environments. No nice icon in my testing on Kubuntu 24.04, alas.