No, it's an ad forcing you to download a malware obfuscating the user as Firefox update. It has been reported a ton of times.

Firefox updates itself through secure and encrypted connection with Mozilla's cloud.

. 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 website of the True Owner of the program in question. For example, to check out Firefox, go to https://www.mozilla.org {web link}

You can 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}

Good call it is malware.

Firefox updates never use that method,

• See Update Firefox to the latest release

Note Firefox should update from Fx47 to Fx48 on or after 2nd August

Note such links as in your post are personalised and others can not see these files.

If you have the file take care not to run or open it. If you do have the file somewhere safe and are able to try submitting it to virustotal.com for scanning and post back with the link they advise you of. {They advise who recognises files as malware, and pass details on to those AV companies}

Most of the fake update files have been .js files recently I wonder if thy have changed the malware file.