Or maybe using new "Web Apps" feature like MacOS has to turn web app into desktop.
<https://wiki.triplescripts.org/wiki/NOT#Not_a_cloud_IDE>
The trick is to untangle the mental equivalence of runs-in-the-browser versus mobile code (code on demand) and/or cloud-thingy-accessed-via-thin-client, which are all orthogonal concepts. To often these get confused. But just like you give people a Java, Python, whatever bundle comprising an app that targets its associated runtime, you can give people a bundle to download and launch from their own computer where the $RUNTIME it's meant to be launched with is /usr/bin/firefox (or whatever).
(And no, this doesn't require browser support for unstable/experimental APIs like Chrome's newest proposed APIs for filesystem access. There are ways to get by with HTML5 stuff that's well-supported by every mainstream browser released in this decade.)