- Go to settings and search for "search engines" / right click the place where website addresses are displayed (search bar) and click edit search engines.
- Under "Other search engines" click add and fill in as follows
a) Search engine: Ecosia
b) Keyword: e
c) URL with %s in place of query: https://www.ecosia.org/search?q=%s
- Go on the search bar and type "e " and then you'll be using Ecosia. Unfortunately, the settings do not allow for it to be truly default although it does get really close.
Here's the same process with StartPage if you would like illustrations: https://support.startpage.com/index.php?/en/Knowledgebase/Article/View/277/13/how-do-i-add-startpage-to-opera-as-a-default-search-engine