The icon collection at present is skimpy and often unrelated to the bookmarks.
Suggest a number of new Icon collections in the same style:
1) World Flags icons
2) Great Cities Icons (Arc de Triomphe for Paris, Big Ben for London, the Onion topped buildings for Moscow, etc.
3) Sports activities and Sports Team icons worldwide.
4) Hobbies like Photography, Play Station, Painting, Guitar Playing, Stamp Collecting, Cats, Dogs, Sailing, Hunting, etc.
5) Money & Finance related symbols. Banks, Wall Street, Currency Symbols, Money Transfer, etc.
6) Brand names and logos like Apple, Google, Microsoft, Salesforce, Nikon, Canon, Ford, GM, Mustang, BMW, United Airlines, Delta, Iberia, etc.
7) Typical buildings. Apartment High Rise, Business Tower, Capitol Building, Bank, Restaurant, Church, Small store, supermarket, school, university, etc.
8) Modes of transportation, Cars, trains, airplanes, cruise ships, taxis,
9) Geographic features like a beach, palm trees, mountains, skyline, hiking trail, world globe, compass, amusement park, stadium
10) Anything else that is common and that users like to create bookmark collections around.
A good freelance graphic designer could crank this out in short order. Size, colors, style have already been determined. Just find public domain photos and convert them to stylized icons.