mixbuilder application and safari extension???

I too experienced the same download, cursor freeze up, need to restart my computer, Safari launching with my normal extensions missing/deactivated. I immediately looked into Safari prefs, found my extensions deactivated and the mixbuilder extension activated. As this was not what I had in mind, I unchecked mixbuilder and rechecked my usual extensions. Once that was done I wanted to see if my extensions functioned as usual, signed into the main application for the first extension, and was asked to change my password. I checked that I was in the appropriate application and not some fabricated look alike. Once secure that that was my site, I changed the password. I then went to apple.support, in search for chat help on my Safar problemi. The chat helper invited me to download a malware app. and run it. (This was a free trial). I did as asked, and within 5 minutes or so, had the culprit mixbuilder with addition 6 or 7 items quarantined, with option to see what they were, and then to delete. They are no longer residing on my computer, and I am again a happy camper. Thank you APPLE-CHAT Support.

A strange coincidence in my application folder is another app called "ExpertFirstExtension.app" which has the very same icon as mixbuilder. I have not yet ruled out whether these two are related in some fashion. They are similar in their limit of Internet information.

The malware app I was invited to try is called "Malwarebytes.app". It instantly found mixbuilder, and additional items, but did not call into quarantine or question "ExpertFirstExtension". If anyone knows what "ExpertFirstExtension" is or does, please leave a note.