Works fine, however it misses an ability to have a delay between opening URLs - they are opened all at once, so if you open too many, they won't even load if the site you're opening them for limits you as a result. This is an essential option for opening many tabs from the same domain.

Also, do NOT use "Do not load tabs until selected" option! Instead of using Firefoxe's native tab discarding, it uses its own mechanism. So I did a test about what would happen if extension is no longer available, by disabling it. Result - all unopened tabs were DELETED. Beware!