When in full-screen and the cursor touches the top screen border the bookmarks bar isn't shown. I don't get the practical reason, just show it by default. By user's customization add the option to show it on Settings, directly on Bookmarks bar options' menu to hide it or both.
While trying to show it by myself I could also move all bookmarks into View more bookmarks menu somehow.
I fixed soon by hiding the bookmarks bar and then showing it.