That's a great and a safe add-on such as demonstration on website virustotal.com, a website that uses a lot of engines against virus and others computer infections...

Scan info: https://www.virustotal.com/#/url/f0cc0473c1ae8add2b64fb5c24e778a65bd31d5300704e5a714d92b8e7a9b986/detection

Tip: How download without install this add-on on firefox?

That's simple -> click on Button with a right mouse button -> [+ Add to Firefox] <- and click in option [Save Link as...] and download it -> [Download File] to save it.