>thousands of tabs open

yeah about that, are you sure they are open and not hibernated? Chrome had proactive-tab-freeze-and-discard , later renamed to proactive-tab-freeze and finally forced On in 80 with no option of turning it off. 'hibernated' tabs are merely a bookmark without loaded content. I dont think this extension would be able to work with non loaded tabs without forcing them all to load. 300 tabs is able to easily eat 16GB of ram, Im scared to think what would happen with 1000 tabs loaded in Chrome.

I remember good old Opera 12.x where you could sit on 200 actually loaded and active tabs and RAM usage was somewhere around 2GB.