mkFirefoxModule: serialize path prefs as strings

Treat Nix paths like plain string preferences when generating user.js so
values such as browser.bookmarks.file are not JSON-quoted twice.

Add a regression case in the Firefox settings test for a path-valued
preference.

modules/programs/firefox/mkFirefoxModule.nix

@@ -75,7 +75,10 @@ let
   userPrefValue =
     pref:
     builtins.toJSON (
-      if lib.isBool pref || lib.isInt pref || lib.isString pref then pref else builtins.toJSON pref
+      if lib.isBool pref || lib.isInt pref || lib.isString pref || lib.isPath pref then
+        pref
+      else
+        builtins.toJSON pref
     );
 
   extensionSettingsNeedForce =

tests/modules/programs/firefox/profiles/settings/bookmarks.html

@@ -0,0 +1 @@
+<!DOCTYPE NETSCAPE-Bookmark-file-1>

tests/modules/programs/firefox/profiles/settings/default.nix

@@ -24,6 +24,7 @@ in
         test = {
           id = 1;
           settings = {
+            "browser.bookmarks.file" = ./bookmarks.html;
             "general.smoothScroll" = false;
             "browser.newtabpage.pinned" = [
               {
@@ -51,8 +52,11 @@ in
 
           assertDirectoryExists "home-files/${cfg.profilesPath}/basic"
 
+          settingsUserJs=$(normalizeStorePaths \
+            "home-files/${cfg.profilesPath}/test/user.js")
+
           assertFileContent \
-            "home-files/${cfg.profilesPath}/test/user.js" \
+            $settingsUserJs \
             ${./expected-user.js}
         '';
     }

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

@@ -2,8 +2,8 @@
 
 
 
+user_pref("browser.bookmarks.file", "/nix/store/00000000000000000000000000000000-bookmarks.html");
 user_pref("browser.newtabpage.pinned", "[{\"title\":\"NixOS\",\"url\":\"https://nixos.org\"}]");
 user_pref("general.smoothScroll", false);
 
 
-