Seems like a really nice concept, but it's pretty much unusable because the keyboard shortcut which is supposed to save the current tab is Alt-T - which is of course the hotkey to open the Tools menu and never reaches the extension.
There are no options to reconfigure the shortcut to one which would actually work, either.
The interface has a few other issues.
When you open its menu, all of your current tabs are in a closed folder for some reason, and you have to expand it manually. The folders are presumably there to show different browser windows, but that doesn't make sense if there is only one browser window open, and it especially doesn't make sense to start it collapsed.
Since the folder has the name of the currently open tab, you might think that saving it would save the current tab, but instead it saves your entire window.
Opening a group of saved tabs will open them in a new window rather than as tabs in the current window, and again there's no option not to do this.
There also doesn't appear to be any way to "pop" a tab from the list, e.g. open it and remove it from the list.
Basically, the extension needs a lot of options to make it usable, starting with the ability to customise the keyboard shortcuts, and going from there.