Editing and saving a page in the Baow add-on creates a zombie compartment. Saving a new page replaces the previous zombie compartment. I'm not entirely sure how much is required to reproduce this. I've only tried it with hiding several elements, highlighting part of the page, and saving. Some of those steps may be optional. Not CCing author as none of their provided email addresses have Bugzilla accounts, but they've been notified via AMO.
Chased developers via info request.
The add-on has been downgraded to preliminary approval pending the memory leak fix.
Closing bug as developer hasn't responded and addon has already been downgraded. We can reopen if there is any further activity or response from the developer.