No popup text for boxed-F icon in book where-to-find list entries

Description of your request or bug report:

in the where-to-find list on a book page, clicking on the boxed-N brings up a popup (“Natively recommends this provider!”), similarly the boxed-E (“eBook provider”), but there is no popup for the boxed-F. I think this should have a “full furigana” explanatory popup.

Example book with this: セーラー服と機関銃 | L30

Trello link: (leave in blank)

Approved… for when I get the time