Looks like you have installed some free software from internet along with that ilivid download manager comes bundled up,
and it is popping up again and again as ilivid download manager files need to be downloaded, see Uninstall software option in windows to check if any traces of ilivid download manager are there, if you find any remove it.
Thanks all, the problem was a program called "Installmate" a browser hijacker.
The problem was solved by
1. Scanned the PC with AV Mcafee and Malwarebytes antimalware and selected clean option.
2. Reinstalled FF after completely uninstalling the previous version.