**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
warnForTextDifference(textNode.nodeValue, text);
      }
    }
    return isDifferent;
  },
  warnForDeletedHydratableElement(
    parentNode: Element | Document,
    child: Element,
  ) {
    if (__DEV__) {
      if (didWarnInvalidHydration) {
        return;
      }
      didWarnInvalidHydration = true;
      warning(
        false,
        'Did not expect server HTML to contain a <%s> in <%s>.',
        child.nodeName.toLowerCase(),
        parentNode.nodeName.toLowerCase(),
      );
    }
  },
  warnForDeletedHydratableText(parentNode: Element | Document, child: Text) {
    if (__DEV__) {