--- firefox-81.0.1/build/mach_initialize.py.old	2020-10-06 14:16:06.212974910 +0200

+++ firefox-81.0.1/build/mach_initialize.py	2020-10-06 14:19:03.313179557 +0200

@@ -507,7 +507,10 @@ class ImportHook(object):

         # doesn't happen or because it doesn't matter).

         if not os.path.exists(module.__file__[:-1]):

             if os.path.exists(module.__file__):

-                os.remove(module.__file__)

+                try:

+                    os.remove(module.__file__)

+                except:

+                    pass

             del sys.modules[module.__name__]

             module = self(name, globals, locals, fromlist, level)