I have been playing with Firefox and Vivaldi as private browsers recently and am very happy with Vivaldi. While Firefox has been around for a long time and I have used it frequently, it has a tendency to become slow and unresponsive. Vivaldi works on Windows and Linux machines but not on Android. Firefox works on all three operating systems.
As an alternative to Google, Yahoo and Bing, I have been using startpage.com. It hides my searches from the big three while at the same time using google's search engine. It does a fair job of searching the web. Duckduckgo.com does not return as many detailed results as startpage.com; google.com wins the search prize but fails the privacy test.
I still find that in about 5% of the searches, I still use google.com to find those obscure sites that are not retrieved by startpage.com.