![Screenshot 2019-12-16 10 51 05](https://user-images.githubusercontent.com/793565/70934095-fd91ed80-1ff1-11ea-93b5-746e816585ec.png)
There's seems to be circumstances where unmounted DOM/Fibers are kept alive by React DevTools. They're kept alive in `primaryFibers`:
https://github.com/facebook/react/blob/34527063083195558f98108cde10b5d6ad0d6865/packages/react-devtools-shared/src/backend/renderer.js#L772

It seems like a WeakSet would be appropriate and would remove the leak. Otherwise we'd need to understand why recordUnmount isn't called.

CC @bvaughn  
I
           a
          forceFallbackForSuspenseIDs.has(id)),
       C
      canViewSource,
       D
      hasLegacyContext,
      key: key != null ? key : null,
      displayName: getDisplayNameForFiber(fiber),
      type: elementType,
       I
       T
      context,
      hooks,
      props: memoizedProps,
      state: showState ? memoizedState : null,
      errors: Array.from(errors.entries()),
      warnings: Array.from(warnings.entries()),
       L
      owners,
       L
      source: _debugSource || null,
      rootType,
      rendererPackageName: renderer.rendererPackageName,
      rendererVersion: renderer.version,
    };
  }
  let mostRecentlyInspectedElement: InspectedElement | null = null;
  let hasElementUpdatedSinceLastInspected: boolean = false;
  let currentlyInspectedPaths: Object = {};