For me this addon completely breaks browser search.
If I type a search query into the search bar it just opens a startpage container with no search term in it. If I type the same search into that window it opens another empty startpage container - etc,etc ad infinitum. No more searches possible until I disable the addon.
Shame really because I like the idea of it a lot, but it just doesn't work as it should.
Edit. Thank you for the response, I deleted my startpage search and added the official addon that you mentioned and now it seems to work as it should!!
I can't explain that one.
Incidentally both google search and bing search worked normally, startpage search has now been fixed, and ddg search first opens an empty search page but typing the search into the empty page generates the required results.