Re: [PATCH 0/13] MR3597: mshtml: Implement Cycle Collection for all mshtml objects (dispex), part 5.

[Gabriel Ivăncescu (＠insn)]

It's possible that an event task is still pending to be processed. Tasks
don't hold ref to the XHR, but they do possibly grab it once processing
starts.

This wasn't an issue before because we called remove_target_tasks
immediately when ref reached 0. But gecko's CC doesn't necessarily call
unlink/delete_cycle_collectable immediately when ref reaches 0, it
usually delays it.

So a task could get processed between ref reaching 0 and the CC actually
cleaning it.