Yeah but check about:policies carefully every time you edit that file. If there is even the tiniest syntax error in policies.json, Firefox silently ignores the

Yeah but check about:policies carefully every time you edit that file. If there is even the tiniest syntax error in policies.json, Firefox silently ignores the entire file. The only way to know this happened is by checking about:policies. Mozilla had to be dragged, kicking and screaming, into providing any kind of stability guarantee for configuration options. "Policies" are just configuration options that have been blessed with this stability guarantee. But Mozilla is still throwing a tantrum over having to provide it...