READ THIS FOR TAB URL RECOVERY: It's a pretty fantastic Add-On, exactly what I always had designed in my mind, thinking I'd have to be the one to develop it. But it tends to lose the URL of SOME of the suspended tabs, which makes it extremely difficult to keep using. (I'm running Firefox Quantum 61.0.1 on Win 7). There is a hack/workaround for getting the URLs back though for anyone interested. Just right click on the tab that lost the URL, and click Duplicate, and a properly duplicated tab will appear at the original URL. Also, it seems like this add-on is doing some extra funky stuff with the firefox memory config to help keep the memory low, but whatever the reason it is breaking pages that aren't inactive or suspended. As best I can tell the pages seem to be losing their cached memory states, causing them to need to be reloaded.