Doesn't work at all, after it scanned, I clicked download then it greyed out the button and says Downloading... But nothings happening, I left my PC running for 3 hours thinking it would be finished by then but it didn't.

Once you hit "scan" it slows down Firefox to an absolute crawl (clicks take very long to register) for at least a quarter hour before eventually crashing it totally. Restarting Firefox & then hitting "scan" in the extension, again froze Firefox.