This add-on leaks compartments of some of the webpages it scans and blocks cookies/ad-tracking on. The issue wasn't picked up on the first version uploaded (I probably overlooked it) but I've now made them aware of it. I'll send them a message directing them to this bug shortly. It can be replicated by opening some webpages and clicking on the addon's toolbar button to show the popup then closing the tab. about:memory?verbose shows references to these closed tabs still.
Thanks andrew. We are looking at this issue now.
Thanks for those clear instructions to reproduce this issue. We have fixed it and will submit for review after some testing.
Current version, 2.0.5 doesn't have memory leak anymore so closing.