Please disable/remove your extension SpeedTest 100.0.0 (@Speedtest) Use this Url instead http://www.speedtest.net/ Please run https://www.malwarebytes.com/mac/ https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware run more than 1 scanner as each uses diff tech. Save your Reports. If doing it your self Google each one as do not want to delete something useful. If need help : https://forums.malwarebytes.com/topic/9573-im-infected-what-do-i-do-now/ Post in 1 forum only and wait. If there is any way to reinstall your video card drivers I would think about it. Some errors showing. Thanks for having send info on. Made this easy. G'luck Run the anti-malware programs ....... You could also uninstall and reinstall (profile is saved) https://fileforum.betanews.com/detail/Mozilla-Firefox-for-Mac-OS-X/1032985422/3 (they get it a day before goes on Mozilla Servers.) Final 57 Release Full version Installer or it updates 56.0.2 Note : Legacy Extensions will be disabled and or removed. Please let us know if this solved your issue or if need further assistance.