I could not find anything on this. How did this come to you?

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.

If you still have the XPI file then your can try to inspect the manifest.json file in this XPI file with an archive manager (a XPI file is a ZIP archive).