It would be very helpful if you can add a symbol to the toolbar so people can disable the extension much easier. Apart from this issue plug-in is very good and works on macOS High Sierra - Firefox 87 developer edition.

Helps give a giant middle finger to Google for the few times I begrudgingly find myself using them instead of Duck Duck Go.

This add-on is a must for the privacy conscious web-searcher of today. It's incredibly useful to be able to use the world's best internet search engine without Google being able to track my search history and tie it to my other Google accounts. Works every time and allows me to stay logged into Gmail and Maps.

Works very well, at least for latest Waterfox.
Allows me to enable Web Activity tracking (to get Google News view history/tailoring) without tracking all searches (those should be separate options, Google!).
Whether you use this extension or not, I suggest disable "Web & App Activity" for Google.com searches and apps (unless want for Google News, etc.) at:

https://myaccount.google.com/activitycontrols

Does not work anymore. Can someone please tell me a good alternative?

Searchonymous not compatible with FF ESR version
An update is necessary