Current patch versus new patch. Seems like the function signature has changed slightly:

--- pkgs/applications/networking/browsers/firefox/env_var_for_system_dir-ff111.patch	2024-08-10 21:13:22.142083987 +0200
+++ pkgs/applications/networking/browsers/firefox/env_var_for_system_dir-ff133.patch	2024-10-29 21:25:17.412737463 +0100
@@ -10,13 +10,13 @@
  #include "prprf.h"
  
  #include "nsIAppStartup.h"
-@@ -309,7 +310,8 @@ static nsresult GetSystemParentDirectory(nsIFile** aFile) {
+@@ -297,7 +297,8 @@ static nsresult GetSystemParentDirectory(nsIFile** aFile) {
        "/usr/lib/mozilla"_ns
  #    endif
        ;
--  rv = NS_NewNativeLocalFile(dirname, false, getter_AddRefs(localDir));
+-  rv = NS_NewNativeLocalFile(dirname, getter_AddRefs(localDir));
 +  const char* pathVar = PR_GetEnv("MOZ_SYSTEM_DIR");
-+  rv = NS_NewNativeLocalFile((pathVar && *pathVar) ? nsDependentCString(pathVar) : reinterpret_cast<const nsCString&>(dirname), false, getter_AddRefs(localDir));
++  rv = NS_NewNativeLocalFile((pathVar && *pathVar) ? nsDependentCString(pathVar) : reinterpret_cast<const nsCString&>(dirname), getter_AddRefs(localDir));
  #  endif
  
    if (NS_SUCCEEDED(rv)) {