firefox manual add search engine

1. Open a new tab and type about:config in the address bar
2. In the search box type: browser.urlbar.update2.engineAliasRefresh
3. Click on the little + symbol on the right. This is what it should look like after you pressed it: boolean true value after pressing plus sign
4. Go to firefox Settings → Search. Or enter this in the address bar: about:preferences#search
5. In the "Search Shortcuts" section you should notice a new "add" button.

参考

https://superuser.com/questions/7327/how-to-add-a-custom-search-engine-to-firefox