Could you check all of the various bookmark lists to see whether this is common to all of them, or only affects particular ones? That might help in identifying the issue.

• Bookmarks button on the toolbar (the right half of the combined star/bookmarks button) > Bookmarks Toolbar flyout menu

• Bookmarks menu on the classic menu bar, if you display it

• Bookmarks sidebar (Command+b, or open from the bookmarks button > View Bookmarks Sidebar)

• Library dialog (Command+Shift+b, or at the bottom of the list from the bookmarks button > Show All Bookmarks)

Are these two computers connected through Firefox Sync or do you maintain the bookmarks on each one separately?

THe fly out doesn't work on any of them.

No I do not use sync. However, I discovered something else.

When I look at all bookmarks and select the blog folder - see 2 images - there is a difference. The correct one is the one with feed location st the bottom. The one that doesn't work does not have this.

Problem solved. I found out I had to subscribe to the page. I did this originally, but I exported my books as html and when I reimported them the subscription turned into a regular bookmark.

Oh I see, these are RSS feeds AKA "Live Bookmarks". In the sidebar, they correctly show they can be expanded as folders, but on the toolbar and in the library, they do not.

Okay... why is that? Hmm... (no time to research right now, but hopefully someone else knows why)

Edit: Our posts crossed and your post has the solution: https://support.mozilla.org/questions/1005643#answer-589565