Is that a the full MSE or a lesser version? That version doesn't have anti-spyware that I know of so if that is having issue then you need to contact Windows Support as that isn't a firefox software.

You may have ad/mal-ware. 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. Each works differently. If one program misses something, another may pick it up.