Hi As far as I can see, my.com is a legitimate site, however I recommend that you have a read of this [https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware article] that will not only provide some guidance around protecting your installation of Firefox from malware, but also has a link to this [https://support.mozilla.org/en-US/kb/how-to-set-the-home-page page] that will help you to reset your home page. I hope this helps, but if not, please come back here and we can look into another option for you