**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
} else if (propKey === DANGEROUSLY_SET_INNER_HTML) {
          const rawHtml = nextProp ? nextProp[HTML] || '' : '';
          const serverHTML = domElement.innerHTML;
          const expectedHTML = normalizeHTML(domElement, rawHtml);
          if (expectedHTML !== serverHTML) {
            warnForPropDifference(propKey, serverHTML, expectedHTML);
          }
        } else if (propKey === STYLE) {
          
          extraAttributeNames.delete(propKey);
          const expectedStyle = CSSPropertyOperations.createDangerousStringForStyles(
            nextProp,
          );
          serverValue = domElement.getAttribute('style');
          if (expectedStyle !== serverValue) {
            warnForPropDifference(propKey, serverValue, expectedStyle);
          }
        } else if (isCustomComponentTag) {
          
          extraAttributeNames.delete(propKey.toLowerCase());
          serverValue = DOMPropertyOperations.getValueForAttribute(
            domElement,
            propKey,
            nextProp,
          );
          if (nextProp !== serverValue) {
            warnForPropDifference(propKey, serverValue, nextProp);
          }
        } else if (DOMProperty.shouldSetAttribute(propKey, nextProp)) {
          if ((propertyInfo = DOMProperty.getPropertyInfo(propKey))) {