Why does Firefox tell me
Content Security Policy: Couldn’t process unknown directive ‘require-sri-for’
when Mozilla's documentation says they've implemented it?
The meta tag Firefox is complaining about:
<meta http-equiv="Content-Security-Policy" content="require-sri-for script;"/>
As of version 69, Firefox no longer supports the require-sri-for CSP due to concerns about standardization status. The original answer below is only valid for versions 49-68.
If you look at the compatibility tables you will see that firefox has a flag which labels this functionality as "User must explicitly enable this feature." To quote:
From version 49: this feature is behind the security.csp.experimentalEnabled preference (needs to be set to true). To change preferences in Firefox, visit about:config.
