Extensions 1-Click YouTube Video Downloader 4.0.4 (YoutubeDownloader@PeterOlayev.com) The link is from the Extension you installed : Copy/Paste about:addons into the Address Bar then Enter. Under Extensions you should find it. Extensions are in your Profile and not in the Program Files. Possibly should have asked 1st. See if there is a option to turn it off in the Extension or if it is in Start Menu and check under Start Up. https://addons.mozilla.org/en-US/firefox/addon/1-click-youtube-video-downl/ There is a Abuse Link on the site that comes back to Mozilla you need to look at terms of service and Mozilla Policy to figure out if that is a option. You have noticed I have not mentioned yet uninstall. Ok, Disable it or uninstall it. Then : Please use more than 1 scanner as each uses diff tech : https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware Save your Report and google each before deleting anything as do not want to delete something you need, If need help : https://forums.malwarebytes.com/topic/9573-im-infected-what-do-i-do-now/ Post in only 1 forum, then wait. Strongly recommend keeping the logs, do not delete anything and go to the Forum for help. Uninstall any Torrent Clients and move off the desktop any files you do not want looked at. It is painless, lots less than this maybe it seems. Suggest Ant Downloader instead. Seems popular. Please let us know if this solved your issue or if need further assistance.