**Do you want to request a *feature* or report a *bug*?**
*Feature*

**What is the current behavior?**
In Firefox the `dialog` element is not implemented. We use a polyfill to be able to support it. Everything works well. But React warns that the `dialog` element is unrecognized, and this on each page load, which is quite useless (for this specific case).
I would like the possibility to disable the  warning but only for some elements. So the utility of this warning remains when the developer mistype the component name.

**What is the expected behavior?**
Once we specified which tag are "accepted/normal" React will not warn on specified unrecognized tags.

**Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?**
React 16
Firefox 57

In previous versions there was no warning.

Is this clear enough? Do you need any other information?
Cheers
validateProperties: validateInputProperties,
  } = ReactDOMNullInputValuePropHook;
  var {
    validateProperties: validateUnknownProperties,
  } = ReactDOMUnknownPropertyHook;
}
var didWarnInvalidHydration = false;
var didWarnShadyDOM = false;
var listenTo = ReactBrowserEventEmitter.listenTo;
var registrationNameModules = EventPluginRegistry.registrationNameModules;
var DANGEROUSLY_SET_INNER_HTML = 'dangerouslySetInnerHTML';
var SUPPRESS_CONTENT_EDITABLE_WARNING = 'suppressContentEditableWarning';
var CHILDREN = 'children';
var STYLE = 'style';
var HTML = '__html';
var {Namespaces: {html: HTML_NAMESPACE}, getIntrinsicNamespace} = DOMNamespaces;
if (__DEV__) {
  var warnedUnknownTags = {
    
    
    
    
    time: true,
  };
  var validatePropertiesInDevelopment = function(type, props) {
    validateARIAProperties(type, props);
    validateInputProperties(type, props);
    validateUnknownProperties(type, props);
  };
  var warnForTextDifference = function(serverText: string, clientText: string) {