Pretty good but has some usability issues. Primarily, the list scrolls to the bottom whenever I make a new tab. Also it's a shame you can't double-click to open a new tab, or middle-click to close a tab (and remove the close button at the end). It doesn't show whether a tab is loaded or not. It works well with Containers, showing the icon at the end - though it would be really cool if you could filter the list by container (i.e. an option to show one container at a time).

Reply: I installed the pre-release (2.1.0a1) but there's no difference re double-click or middle-click. Nor does that about:config change do anything re showing if a tab is unloaded - it only shows if it is loading. Fair enough re containers.