Did you download Firefox from Mozilla.org ? Did you respond to any 'update' pop-ups/messages?

Let’s do a full clean re-install;

Download Firefox For All languages And Systems {web link}

Save the file. Then Close Firefox.

Using your file browser, open the Programs Folder on your computer.

Windows: C:\Program Files C:\Program Files (x86)

Mac: Open the "Applications" folder. https://support.mozilla.org/en-US/kb/how-download-and-install-firefox-mac

Linux: Check your user manual. If you installed Firefox with the distro-based package manager, you should use the same way to uninstall it. See Install Firefox on Linux; https://support.mozilla.org/en-US/kb/install-firefox-linux

If you downloaded and installed the binary package from the Firefox download page, simply remove the folder Firefox in your home directory. http://www.mozilla.org/firefox#desktop ++++++++++++++++++++++++++++ Look for, and remove any Mozilla or Firefox program folders. Do not remove the Mozilla Thunderbird folder if there is one.

Do Not remove the profiles folder.

After rebooting the computer, run a registry scanner if you have one. Then run the installer. +++++++++++++++++++++++++++ If there is a problem, start your Computer in safe mode and try again.

http://encyclopedia2.thefreedictionary.com/Linux+Safe+Mode This shows how to Start all Computers in Safe Mode; Free Online Encyclopedia

Called a very poor A/V program that no longer works to protect rather it has become a malware itself. Advise get a better program that doesn't think it can think for you.

Thanks for the responses. Maybe I did not properly explain what happened. Norton 360 blocks the so-called attack on firefox.exe or whatever. When I run Norton scan, Norton power eraser scan and malwarebyes they find nothing and firefox works just fine., When firefox notifies me that an update is available I get from the notification or from about firefox(usually from about firefox). Have also scanned the firefox folders separately for malware and viruses. By the way, WestEnd what is your suggestion for a better A/V program? I find Norton 360 to be much better than McAfee. Thanks for your suggestions.

Personal opinion : With Windows' built-in Defender and the safest browser on the planet :  it's like being in Fort Knox   !

See : http://tech.firstpost.com/news-analysis/ex-mozilla-firefox-developer-says-anti-virus-software-does-more-harm-than-good-359798.html

And also :
https://www.howtogeek.com/239950/dont-use-your-antivirus-browser-extensions-they-can-actually-make-you-less-safe/

Does this attack come from any website, some, one?

Happy112, interesting info. Have seen Firefox block some things, but, in this case I was updating and using firefox and the intrusion was blocked by Norton, not firefox.

marv6 said

Norton 360 blocks the so-called attack on firefox.exe or whatever.

Norton 360 was discontinued in 2014 and replaced by Norton Security.

James, wow! was not aware of that. Norton is still charging me yearly and is still updating the virus definitions at this time. It has been awhile since they have updated the version and I checked and it said I was running the latest version. Guess it is old now.

James said

Norton 360 was discontinued in 2014 and replaced by Norton Security.

Norton 360 is still supported and updated. The last major update was this month.

FredMcD said

James said

Norton 360 was discontinued in 2014 and replaced by Norton Security.

Norton 360 is still supported and updated. The last major update was this month.

With some updates for those who continue to use it yes however it is indeed discontinued as they are no longer selling the product, or updating the core program components since 2014 and was replaced by Norton security.