diff --git a/widget/gtk/WidgetUtilsGtk.cpp b/widget/gtk/WidgetUtilsGtk.cpp
--- a/widget/gtk/WidgetUtilsGtk.cpp
+++ b/widget/gtk/WidgetUtilsGtk.cpp
@@ -443,11 +443,10 @@
 // Documentation for some of those can be found in:
 //
 // https://wiki.archlinux.org/title/Environment_variables#Examples
 // https://wiki.archlinux.org/title/Xdg-utils#Environment_variables
 const nsCString& GetDesktopEnvironmentIdentifier() {
-  MOZ_ASSERT(NS_IsMainThread());
   static const nsDependentCString sIdentifier = [] {
     nsCString ident = [] {
       auto Env = [](const char* aKey) -> const char* {
         const char* v = getenv(aKey);
         return v && *v ? v : nullptr;