Currently, isolated trees are cleaned up like so: 1. AXObjectCache::~AXObjectCache() calls AXIsolatedTree::removeTreeForPageID(*m_pageID) 2. AXIsolatedTree::removeTreeForPageID calls AXIsolatedTree::queueForDestruction 3. AXIsolatedTree::queueForDestruction sets m_queuedForDestruction to true 4. The next time AXIsolatedTree::applyPendingChanges() is called, the tree is destroyed if m_queuedForDestruction is true Because this relies on AXIsolatedTree::applyPendingChanges() being called organically (i.e. an AX client requesting an attribute from a wrapper that is part of the soon-to-be-destroyed tree), it's possible we could never clean up a tree queued for destruction. AXIsolatedTree::queueForDestruction should probably set some internal timer to clean the tree up so we don't rely on AX clients requesting data from a soon-to-be-destroyed wrapper.