**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
extraAttributeNames.delete(propertyInfo.attributeName);
            serverValue = DOMPropertyOperations.getValueForProperty(
              domElement,
              propKey,
              nextProp,
            );
          } else {
            let ownNamespace = parentNamespace;
            if (ownNamespace === HTML_NAMESPACE) {
              ownNamespace = getIntrinsicNamespace(tag);
            }
            if (ownNamespace === HTML_NAMESPACE) {
              
              extraAttributeNames.delete(propKey.toLowerCase());
            } else {
              
              extraAttributeNames.delete(propKey);
            }
            serverValue = DOMPropertyOperations.getValueForAttribute(
              domElement,
              propKey,
              nextProp,
            );
          }
          if (nextProp !== serverValue) {
            warnForPropDifference(propKey, serverValue, nextProp);