Be careful with old versions!
These versions are displayed for reference and testing purposes. You should always use the latest version of an add-on.
I've ported it to the new WebExtension system so it will start working again.
Unfortunately there isn't currently a way to customize the keyboard shortcuts within WebExtensions, so everyone's keyboard shortcut is back to ctrl-shift-1 (Windows) or cmd-shift-1 (macOS).
New in this version is a toolbar button that does the same thing as the shortcut. You can get rid of it using the customize feature of the menu.
Most Recent Tab should now work as expected when you have multiple windows.