Hi There is a possibility that this is unfortunately being caused by malware. As a first step, I recommend making sure that both Firefox and your copy of Windows is completely up to date. Further to this, run a full malware scan. Windows Defender can be a good starting place for this. Look out for any other apps or games your have recently installed in your device. For further information and support, please have a look at: https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware