add toggle sidebar functionality

[ipatch]

i use firefox and often pop open the sidebar to quickly navigate to a page in my history and sometimes in my bookmarks. while using firefox i often have my right hand on the mouse, and my left hovering/resting on the keyboard. it'd be nice to be able to toggle the sidebar in firefox with this extension without having to use the default control+h because with my current key layout it requires removing hand from mouse to use that keybinding, and if i could just map something along the lines of ` it'd speed things up quite a bit for my daily use. as i often use z to go back in the browser history.

thanks for the plugin. 🙏 it's definitely saved me several clicks. 🖱