Comment 113 for bug 2046844

Also note that even the system's build of Bubblewrap is not granted the ability to bypass user namespace restrictions as that would allow the restrictions to be bypassed by any application. Doing this to your own build of Bubblewrap will pose the same security issue. If you can avoid doing things the way you're doing, that would be best, otherwise just turning off the restriction or granting your build of Bubblewrap an exception at install time is probably the best you can do.