Hi  !

These are not from Mozilla, but this is a technique, used by cyber criminals to install adware and a potentially unwanted programs on users computers.

Just to be on the safe side, would you do this please : Go to the 3-bar menu (or   'Tools') => Addons => Extensions and look for any unfamiliar or suspicious looking extensions.

When you find any : remove them.

Do the same in Windows' Control Panel => Programs.

However :   most malware will be 'hiding' somewhere , so let's run malware scans :

Further information can be found in this article :
https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware?cache=no

Run most or all of the listed malware scanners.
They all work differently   -   what one program doesn't pick up, the other might.

Also see : https://malwaretips.com/blogs/java-software-critical-update-removal/

I was wondering, especially since the download site was: eicharesponsecenters.net and it was not reachable in any browsers.

Will do the scans and report back.

rzn6jw said

Will do the scans and report back.

Take all the time you need.