![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  
} else {
      forceFallbackForSuspenseIDs.delete(id);
      if (forceFallbackForSuspenseIDs.size === 0) {
         L
        setSuspenseHandler(shouldSuspendFiberAlwaysFalse);
      }
    }
    const fiber = idToArbitraryFiberMap.get(id);
    if (fiber != null) {
      scheduleUpdate(fiber);
    }
  }
   Remember if we're trying to restore the selection after reload.
   In that case, we'll do some extra checks for matching mounts.
  let trackedPath: Array<PathFrame> | null = null;
  let trackedPathMatchFiber: Fiber | null = null;
  let trackedPathMatchDepth = -1;
  let mightBeOnTrackedPath = false;
  function setTrackedPath(path: Array<PathFrame> | null) {
    if (path === null) {
      trackedPathMatchFiber = null;
      trackedPathMatchDepth = -1;
      mightBeOnTrackedPath = false;
    }
    trackedPath = path;
  }
   We call this before traversing a new mount.
   It remembers whether this Fiber is the next best match for tracked path.
   The return value signals whether we should keep matching siblings or not.
  function updateTrackedPathStateBeforeMount(fiber: Fiber): boolean {