Does what it says. I looked at the code (scripts/bg.js inside of the .xpi for version 0.0.1), and it's four lines of code that add an onClicked callback that prefixes the string 'https://12ft.io/' to the current tab's url and then loads it. Simple, safe.

So far (1 day), it seems to work just fine for me, so many thanks to the developer !
Would be great if Mozilla could help checking the safety of it though.

beautiful

Perfect. Does what it says without flaw.