diff -up firefox-78.2.0/python/mozbuild/mozbuild/controller/building.py.mach-fail firefox-78.2.0/python/mozbuild/mozbuild/controller/building.py
--- firefox-78.2.0/python/mozbuild/mozbuild/controller/building.py.mach-fail	2020-09-09 19:25:18.552930506 +0200
+++ firefox-78.2.0/python/mozbuild/mozbuild/controller/building.py	2020-09-09 19:25:31.081010223 +0200
@@ -591,7 +591,7 @@ class TerminalLoggingHandler(logging.Han
             if self.footer:
                 self.footer.clear()
 
-            self.fh.write(msg.encode("utf-8"))
+            self.fh.write(msg)
             self.fh.write('\n')
 
             if self.footer: