1. There is an Issue on m.youtube.com. After reloading, highlighted text and all chars after in the string, that contains it, disappear. (You will have to trick youtube with any android user agent to open exactly m.youtube.com )
2. Please, create settings for user defined DEFAULT highlighting style, and an option not to open sidebar/tab when new text is marked through context menu. That will add grate overall speed and convenience advantages.
3. As in your speed dial add-on, internal pages are notably slow on notebooks

Thanks for developing.