Hi

Please do not call that number - it is a scam. Mozilla does not provide support over the phone.

This article has some very useful tips and guidance: https://support.mozilla.org/en-US/kb/avoid-and-report-mozilla-tech-support-scams

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 free to use malware scanners. Each works differently. If one program misses something, another may pick it up.