Thanks for the suggestion. It sounded like a good idea, so I wrote the code halfway through, but since there is no API to visually cancel the drag operation, I decided to pass on it this time.
As an alternative, I thought of creating a cancel zone in the corner of the screen and dropping the drag operation there.
Currently, you can interrupt by pressing the ESC key.

検索はFirefox標準の検索エンジンに登録されているものを使用できます。
検索エンジンを追加するにはそのサイトがOpenSearchに対応している必要があり、Twitterは対応しています。（日付などの詳細なパラメータは渡せません。）
検索エンジンの追加方法は複数ありますが、対応しているサイトに移動してアドレスバーを選択すると「今回だけ使う検索エンジン」という項目が出るのでそこで追加するのが簡単です。

I couldn't confirm that in my environment.
Try updating Firefox to the latest version and disabling all other add-ons.

It could be happening only to you, or it could be a problem with the site.
I need specific samples to fix it, so it would be helpful if you could write them down.
The page and selection where the problem occurs, and the URL of the newly opened tab.

They seem to cause problems with the text on the links.
I don't know if everything will work, but I did the update.

This add-on works alone in your browser only.
It does not collect any information. It does not send any information anywhere.
I wrote all the code from scratch, so I am confident this is a secure add-on. The code has also been inspected by Mozzila.

I never thought about what I needed to write about privacy statements.
Should I have insisted that "no information of any kind will be collected?"

Anyway thank you for reviewing it.

Thank you for the report. But I could not confirm that.
It may be interfering with other add-ons. So please try using this add-on only.
If we can find the cause, we can adjust it.

It is not fully customizable, but can be added to any site that uses Open the Search, which can be integrated into Firefox.
Naver is not supported, but Daum can be added.

More information can be found on the Mozilla support page.
https://support.mozilla.org/en-US/kb/add-or-remove-search-engine-firefox