diff --git a/toolkit/mozapps/installer/Packager.pm b/toolkit/mozapps/installer/Packager.pm
index e01e71c4d17..5170cc2d9c3 100644
--- a/toolkit/mozapps/installer/Packager.pm
+++ b/toolkit/mozapps/installer/Packager.pm
@@ -300,8 +300,15 @@ sub do_copyfile
     }
   }
 
+  # Translate: */../../*/bin/*
+  #      into: */../../*/*
+  # (where the *'s are interpreted using shell-notation and
+  #  it matches not only forward slashes but also backslashes.)
+  # $1 = */../../*/
+  # $2 = bin/
+  # $3 = *
   if ($flat) {
-    $destpath =~ s|bin[/\\]||;
+    $destpath =~ s|(.*[/\\]\.\.[/\\]\.\.[/\\].+[/\\])(bin[/\\])(.*)|$1$3|;
   }
 
   # create the destination path if it doesn't exist