Hi,

Thanks for reviewing.

> add option to "auto detect protocol"
Certainly. I should add this feature. A user don't need to choose a protocol if a link is https.

> make dpi scale same as tab
I will think about this later.

> hover on/drag the link to open in sidebar
The former requires injecting a new script to a web page. Basically I don't add a feature like this type.
The latter requires Firefox API but they don't provide the feature currently.

If you have an additional requests, please tell me by modifying this review, sending an e-mail or opening a new issue on GitHub.

P.S.
I tried to add 'make dpi scale same as tab' but it was not able to be done. A sidebar needs to get information of the page in the sidebar but it is not supported by Firefox.
I am working on adding "auto detect protocol". You can check the issue to track the status.
https://github.com/Soushi-Atsumi/Open-in-Sidebar/issues/4