Scammer froze system, showed phone number

While browsing the news in Firefox the page changed to a red background “Alert from the Mozilla Tech Support Team” with number to call 1-844-380-1773. The English in the message wasn’t very good. It froze up my computer, could not even use ctrl-alt-del to access the task manager. Had to power cycle the system to bring it back. First thing I did after that was join this forum. Has anyone else seen this?

It’s a scam number I called it but I’m not sure ?

It’s a scam. I called them and screwed with them and they told me that malware was an antivirus system. They also said they would sell me Indian nuclear codes.