Нафига окно на редактируемой странице? Выбор элемента не конкретный (выбираются все элементы под данным id или class)? В коде не отмечаться место начала редактирования, выделить часть нельзя. И другие элементарные вещи которые вы не удосужились пофиксить.

This extension is the perfect solution for editing and saving the edited CSS styles of any visited webpage. It is easy to use. It allows to edit styles with help of forms or manually edit the CSS code. And after that, the rules are saved and applied to the edited webpage each time it is loaded.

Need better instructions, maybe a video? Is not wanting to work, but idk for real if it's me doing nonsence

So happy to see this finally getting Firefox support. Was using it for a while in Chrome and now while I'am migrating to Firefox happy to see it here as well. Visual editor is amazing.