That's a 'web forgery'. You can use Help > Report Web Forgery ... to report that URL to Mozilla.

I can't know whether this site is secure and authentic or not but I recommend you to always download or update your firefox only from authorized sites only.

Use these sites to download firefox :

• https://www.mozilla.org/en-US/firefox/new/
• https://www.mozilla.org/en-US/firefox/channel/

and also if you have firefox already installed in your system then you can directly update it :

Goto Open Menu(Right on top 3 bar)>Click on Help(at bottom after customize) now Click on "About Firefox " . it will opens a window and automatically started downloading the latest version. Scan your system with a good malware scanner and keep updated your windows.

Whenever in doubt , use close button and ask others .

. Whenever you get a message / popup that software / files need to be updated;

DO NOT USE ANY OF THE PROVIDED LINKS

While this may be a legitimate message, it could also be Malware or a Virus. Any time you want or need to check for upgrades, go to the web site of the True Owner of the program in question. For example, to check out Firefox, go to Mozilla.org. {web link}

You can sent a report to The FBI via their web site Internet Crime Complaint Center (IC3) {web link}

You can also report such a site at; Google Report Phishing Page {web link} which is the same when done while on site by going to Help > Report Web Forgery

Help us safeguard Mozilla’s trademarks by reporting misuse {web link}