Nice. Basically required for Firefox use. (Firefox really needs to add this absolutely normal tab-handling functionality to the browser--Chrome's had it since the beginning.)

This may be the same as a previously existing extension called "Select and Do"? (It's been a while since I used Firefox, but this came up when I searched for that extension which I previously used for this purpose.)

I feel like I may have preferred that one, but I might be completely making this up and this may be the exact same extension with a different name. Who knows.