It seems as though I'm having an issue most others are not encountering, so I hesitate to give a poor rating, but after installing this add-on, I noticed my browser slowed down considerably. Extremely sluggish and frustrating, to the point of being unusable. I verified that this is due to the add-on by using Firefox's Process Manager. The 'Extensions' process hovers at 1-5% CPU usage when I have this extension disabled. When I enable it, it rises to between 50% and 100% CPU usage, and stays that way even 10 minutes after enabling it (which I did to ensure it wasn't just a start-up cost). It drops again within seconds of disabling the extension. I do have a large number of windows open, which may be part of the issue, and my goal was to reduce that number using this extension. However, I could barely get a single tab stashed in 10 minutes, so unfortunately, I'm not going to be able to use this to get to that point. I hope the developer is able to identify the source of the high CPU usage I've experienced, as it otherwise seems to be a very good extension. Will check back in a few months and try again.