diff -pruN firefox-75.0.orig/python/mozbuild/mozbuild/controller/building.py firefox-75.0/python/mozbuild/mozbuild/controller/building.py
--- firefox-75.0.orig/python/mozbuild/mozbuild/controller/building.py	2020-04-10 14:06:41.934514666 +1000
+++ firefox-75.0/python/mozbuild/mozbuild/controller/building.py	2020-04-10 14:11:07.421260179 +1000
@@ -586,7 +586,7 @@ class TerminalLoggingHandler(logging.Han
             if self.footer:
                 self.footer.clear()
 
-            self.fh.write(msg)
+            self.fh.write(msg.encode("utf-8"))
             self.fh.write('\n')
 
             if self.footer: