The warning message is not from Mozilla, and alerts like that are nearly always scams trying to get you to install malware.

You should delete that file and then run a full scan with your anti-virus program, and additionally run some anti-malware programs to ensure that your computer has not been infected. It is best to run several as each will pick up things that the others miss. Some scanners you can try are:

• Malwarebytes - http://www.malwarebytes.org/mbam.php
• SuperAntiSpyware - http://www.superantispyware.com/
• Ad-Aware - http://www.lavasoft.com/products/ad_aware_free.php
• Windows Defender - http://www.microsoft.com/windows/products/winfamily/defender/default.mspx
• Spybot S&D - http://www.safer-networking.org/en/home/index.html

Please don't fell for it and also use Report Web Forgery… so others are warned about this scam in the future.

You should never respond to such a pop-up in any way and avoid clicking any OK or Cancel buttons.
Only trust your own security software.
Such pop-ups are only meant to seduce you do download a program and get infected with malware (virus).
If even using the Close X on the pop-up start a download then you may need to use the task manager to close Firefox and delete sessionstore.js in the Firefox Profile Folder to prevent Firefox from restoring that page on the next start.

Thanks for all the help on this. Firefox is so good at blocking things like this that it took me by surprise, and I wondered if it could actually be from Mozilla. When I received the warning that it was from another computer, I backed out right away, but asked the question, anyway.

I have since deleted the files and since I never started any download, apparently no harm to my computer. At the first opportunity, I will advise Mozilla of this.

SHABBONA_RR

OK, now I'm lost again. I clicked the Report Web Forgery, and get all kinds of information except how I actually do that.

SHABBONA_RR

OK, I figured it out, but I'm not sure Firefox got my report. I hope so

SHABBONA_RR