"Bookmarks" as a reference to the objects should be "bookmarks", p.58

Rev. 788
Ch. 3, § "Bookmarks", p. 58 (PDF p. 60)
Types: capitalisation; style

Manual has:
In Firefox, you can create Bookmarks, which are saved in the web browser and which you can use to navigate back to your picked web pages.

"Bookmarks" is also italicised, which is sufficient emphasis. It is not a proper noun so it shouldn't be capitalised too.

Also, there's the repetition of "which", and use of "picked".

Suggestion:
In Firefox, you can create bookmarks that are saved in the web browser, and which you can use to navigate back to those web pages.