See Help > Extension & Bookmarklets > Bookmarklets, then click on the link to our Extras page (DEVONtechnologies | Handbooks and Extras).
But sometimes the help viewer’s cache of macOS is outdated and causes the above error message but rebooting and/or reinstalling the app should fix this.
However, bookmarklets are optional and rarely necessary (e.g. if a browser doesn’t support extensions).