While helper.exe is a program used by Firefox and other programs, it could be the file is contaminated, of a fake.

You may have ad / mal-ware. Further information can be found in the Troubleshoot Firefox issues caused by malware article.

Run most or all of the listed malware scanners. Each works differently. If one program misses something, another may pick it up.

Antivirus clients have done the occasional false positives on something in Firefox folder on Windows, however it was often fixed in a definition update from said antivirus.