Works great, though I wish it has an option to both search and copy the search term to clipboard.

If possible, It would be better if user can edit their custom search engine. (to instead of the Built-in engine)

like:
Google Translate：https://translate.google.com.tw/?hl=zh-TW#auto/zh-TW/{searchTerms}
Cambridge ：http://www.learnersdictionary.com/definition/{searchTerms}

or like: https://i.imgur.com/Wr4O2GF.png

It is good drag tool. Can it use the firefox's default search engine instead of the extension's built-in

I have to admit I just recently installed it, but from the looks of it this seems to be the real deal: both in terms of how it functions straight out of the box with default setup, and also from the seemingly very robust and versatile setting. It already is better than Fire Drag is, simply because Facebook Messenger functions as it should.

検索の為の手順がドラッグ&ドロップで済むのがとても楽でいい。
プレーンテキストのURLを選択してそのまま開けるならさらにいいかも。

Since upgrading to Quantum, I lost my original drag & go add on. This one does exactly what my original one did (especially open a search in a background tab) as well as offers some really nice image options (save or search).

Very happy thus far!