That site is not part of Mozilla, and the file you can download from there is not Firefox, it is only 1MB whereas the actual download for Firefox should be around 16MB.

Checking the mozilla-firefox.exe file against mutiple virus scanners, several detected malware, for details of the scans see https://www.virustotal.com/file/d8811847d7f891df34a5fd1c37826902f4b8d87c3535d2cd00e328ca23d90b5f/analysis/

Thank you TonyE. This is very hopeful. Do you recommend which specific tool to use to detect/remove malware from the .exe file? Again, many thanks

The following Mozilla support article contains some links near the bottom of the article for third-party software that can be used to remove malware from Windows - Troubleshoot Firefox issues caused by malware

Thank you TonyE. You're response was not only prompt but thorough. You have been extremely helpful and I am grateful

I had the same thing happen, however, I never opened the program. I realized my mistake once it had downloaded to my computer and deleted it without opening or running it. Do I still need to worry?

cal259 you should have no problems, but it is always a good idea to run regular scans with anti-malware programs.

As far as I can tell, this program appears to install a toolbar that may track web usage and push adverts to users.

It's adware - Malware Bytes will fix it.

Guessing you got the conduit search take over too then...