Hi there, thanks for the review! I've been using 67.0b10 and it's working fine for me. Please feel free to get in touch with more details if possible.

As for deleting cookies, your comment prompted me to switch to use a different kind of storage system for the next version of the addon. It's currently in-the-works. Stay tuned for that.

Thanks,
Simon

UPDATE: I uploaded 1.0.6 earlier tonight. It uses a better storage API and should address your problem! It's pending approval before being released right now.