Firefox before version 57 allows users to open new tab from address bar using an extension (e.g. TabMixPlus). TabMixPlus is no longer supported. How to make Firefox 57+ to always open new tab from address bar?
(New tab from bookmarks is accessible via
browser.tabs.loadBookmarksInTabs, but I have not find an
about:config entry for new tab from url bar, just an feature request for
UPDATE: Firefox 60 added the missing option to about:config.