Hi there, I'm the developer. I very much appreciate the Feedback, even it's low star haha. About your question, you can turn off the mouse function on the popup page (by clicking the icon). Adding a forward-slash is easy, but it may cause conflict with the Youtube website hotkey.
So far, if applying the mouse function, you need to make sure not to hover the mouse on the video area in case of an unintentionally altered speed. The original idea of the plugin was to change EDM speed precisely and control it from a far distance easily. Very few people use the mouse only to change speed, so I am not sure if I will change the function for now. It will be improved soon and I am still working on it. I welcome more of your feedback and thanks for using it.