Hi billlogan1949, Malwarebytes should have quarantined it. Check the Quarantine tab. If it's there, you can delete it. It will be removed.

Also, take a look at the new Malwarebytes Browser Guard: https://addons.mozilla.org/en-US/firefox/addon/malwarebytes/?src=search

Thanks for getting back so quickly. I'm afraid, having done what you advised, the above address shows in my Web Search. I tried to take a screen shot of it, but it doesn't include the address.

I'm a Windoze user but, here is an article: Troubleshoot Firefox issues caused by malware https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware?cache=no#firefox:mac:fx69 Set for Mac users.

And another site which recommends using Bitdefender Adware Removal Tool: https://junkwareremoval.com/adware/remove-zanzibog-mac-os-x/

My fingers may have been moving faster than my brain, again. If the address is showing in your Search Results or History, it doesn't necessarily mean that you are still "infected". Clearing your Cache, Cookies and History may be all that you need to do.

I've followed both your latest posts and Zanzibog is still shown when I open Firefox, but when I open a new tab Firefox search comes up as normal. I wonder, as a last resort, should I delete Firefox as my browser and reload it presumably losing all my Bookmarks? Or should I simply use Safari as my default browser?

It sounds like this may be set as your Firefox home page. Restore the default home page this article can help you do that.

Bingo! Thanks a lot, that seems to have solved my problem.