diff -Naur firefox-52.9.0esr.orig/toolkit/mozapps/installer/packager.py firefox-52.9.0esr/toolkit/mozapps/installer/packager.py
--- firefox-52.9.0esr.orig/toolkit/mozapps/installer/packager.py	2017-04-11 04:13:24.000000000 +0200
+++ firefox-52.9.0esr/toolkit/mozapps/installer/packager.py	2021-11-07 17:31:56.920859058 +0100
@@ -163,8 +163,10 @@
                                   % resource],
                            extra_linker_path=gre_path,
                            extra_env=extra_env):
-            errors.fatal('Error while running startup cache precompilation')
-            return
+            # errors.fatal('Error while running startup cache precompilation')
+            # return
+            # Ignore the xpcshell errors as it's buggy ATM
+            pass
         from mozpack.mozjar import JarReader
         jar = JarReader(cache)
         resource = '/resource/%s/' % resource