Running via `nix run` doesn't run the nightly

[agoose77]

I'm new to Nix, and specifically don't understand yet the nuances of how the flake standard is interpreted. So, apologies if this is user error.

I tried to run the nightly from this flake using

nix run github:nix-community/flake-firefox-nightly#firefox-beta-bin

This launched my Firefox binary (version 128). So, then I tried nix shell ..., which gave me this PATH:

> echo $PATH
/nix/store/f7pkv8r1zm9hyhzmx2jljxmiy8nf82d6-firefox-variants/bin:...

But this doesn't exist:

> test -d /nix/store/f7pkv8r1zm9hyhzmx2jljxmiy8nf82d6-firefox-variants/bin || echo "Doesn't exist"
Doesn't exist

If I ls around that PATH, I find that /nix/store/f7pkv8r1zm9hyhzmx2jljxmiy8nf82d6-firefox-variants does exist, and try launching the binary directly

> /nix/store/f7pkv8r1zm9hyhzmx2jljxmiy8nf82d6-firefox-variants/firefox-nightly-bin/bin/firefox-nightly --version
Mozilla Firefox 131.0a1

But launching that binary again seems to launch my global Firefox. Only if I invoke the unwrapped binary does it work.

I suspect this might be a my-system thing rather than this-flake thing, but any pointers would be appreciated.