No trouble where a session has just a few tabs.

Where there are many tabs: browser performance can become very poor, for extended periods, when the UI of the extension is used.

I have a few screen recordings, here's the most recent: https://photos.app.goo.gl/MEsmZQ4gkmt5RKDj2

Postscript, 2019-01-28, re: the developer's response (below) … in recent months I haven't tested thoroughly with so many tabs, I'll upgrade my star rating from three to five with an assumption that all is good. Thanks!