1. Create a temporary bookmark (e.g. by pressing ctrl + D, or clicking or the star in the address bar)
2. Open your bookmarks (e.g open the bookmark bar, or press ctrl + B)
3. Right click on the bookmark, and choose "edit bookmark" (or right click, then press "i")
4. Fill the "URL" field with
javascript:window.location='http://sci-hub.se/'+window.location
5. Fill the "keyword" field with "shb" (or whatever you want)
That's it, whenever you write "shb" in the address bar on a page and hit ENTER, it will navigate you to
What do I actually write in the address bar?