Hi,
I see that the latest firefox developer edition dismisses the extension when clicked “enter” from searchbox. Usually it used to opene a new tab with search results. Also I see hyperlinks with
opens a new blank tab along with url tab.
I notice this from latest firefox developer edition only.
One of the extension you can try is
https://addons.mozilla.org/en-US/firefox/addon/duckduckgo-for-firefox/