**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
if (type === 'script') {
        
        
        var div = ownerDocument.createElement('div');
        div.innerHTML = '<script><' + '/script>'; 
        
        var firstChild = ((div.firstChild: any): HTMLScriptElement);
        domElement = div.removeChild(firstChild);
      } else if (typeof props.is === 'string') {
        
        domElement = ownerDocument.createElement(type, {is: props.is});
      } else {
        
        
        
        domElement = ownerDocument.createElement(type);
      }
    } else {
      domElement = ownerDocument.createElementNS(namespaceURI, type);
    }
    if (__DEV__) {
      if (namespaceURI === HTML_NAMESPACE) {
        if (
          !isCustomComponentTag &&
          Object.prototype.toString.call(domElement) ===
            '[object HTMLUnknownElement]' &&
          !Object.prototype.hasOwnProperty.call(warnedUnknownTags, type)
        ) {
          warnedUnknownTags[type] = true;
          warning(