firefox: add nix-prefetch-firefox-extension script

scripts/default.nix

@@ -145,6 +145,10 @@
     print-battery-icon = [ ];
     controller-battery = [ print-battery-icon ];
     mouse-battery = [ print-battery-icon ];
+    nix-prefetch-firefox-extension = [
+      nix
+    ];
+
     _docker-block-external-connections = [
       iptables
       gawk

scripts/nix-prefetch-firefox-extension

@@ -0,0 +1,7 @@
+#!/bin/sh
+
+set -euo pipefail
+
+hash="$(nix-prefetch-url --type sha256 "$@")"
+
+nix-hash --to-sri --type sha256 "$hash" 2>/dev/null

user/firefox.nix

@@ -139,6 +139,11 @@ in
         };
       };
     };
+
+    home.packages = with pkgs; [
+      nix-prefetch-firefox-extension
+    ];
+
     wayland.windowManager.sway = {
       extraConfig = ''
         exec firefox-devedition