[bilkow]

Step 5 onwards don't work on private tabs for some reason. For private tabs you can do all steps up to 4 and then:

5. Tap on the URL bar

6. Type part of the name of the bookmark you chose until it appears in search (in my case eruda works)

7. Tap the bookmarlet

For this to work you need to have bookmark search enabled in settings: Settings -> Search -> Search bookmarks

Also, there seem to be many sites where the widget doesn't appear, but you can try it at google.com.