firefox: use wrapped package

This makes the

    programs.firefox.package

option take a pre-wrapped Firefox package as value if state version is
set to "19.09" or later. This should make the Firefox module work with
a wider range of Firefox packages.

tests/modules/programs/firefox/default.nix

@@ -0,0 +1,4 @@
+{
+  firefox-profile-settings = ./profile-settings.nix;
+  firefox-state-version-19_09 = ./state-version-19_09.nix;
+}

tests/modules/programs/firefox/profile-settings-expected-user.js

@@ -0,0 +1,6 @@
+// Generated by Home Manager.
+
+user_pref("general.smoothScroll", false);
+
+
+

tests/modules/programs/firefox/profile-settings.nix

@@ -0,0 +1,24 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+{
+  config = {
+    programs.firefox = {
+      enable = true;
+      profiles.test.settings = {
+        "general.smoothScroll" = false;
+      };
+    };
+
+    nmt.script = ''
+      assertFileRegex \
+        home-path/bin/firefox \
+        MOZ_APP_LAUNCHER
+
+      assertFileContent \
+        home-files/.mozilla/firefox/test/user.js \
+        ${./profile-settings-expected-user.js}
+    '';
+  };
+}

tests/modules/programs/firefox/state-version-19_09.nix

@@ -0,0 +1,17 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+{
+  config = {
+    home.stateVersion = "19.09";
+
+    programs.firefox.enable = true;
+
+    nmt.script = ''
+      assertFileRegex \
+        home-path/bin/firefox \
+        MOZ_APP_LAUNCHER
+    '';
+  };
+}