18 years now using Firefox and since Places was added in like 2008 I have struggled to make sense of the Places UI. I basically gave up years ago and use the Bookmarks Sidebar, and forget about the "Library" window which is the default for "All Bookmarks". And I hide the Toolbar buttons for Bookmarks to allow for more space for Toolbar Buttons that I do use, for add-ons.

{Ctrl + B} to open the Bookmarks Sidebar, and for each folder there is a Context Menu item for "Sort by Name". With "Bookmarks Menu" folder the entire column will be sorted; but not within each individual folder that you may have added. Each individual folder sorts by itself. IOW, no global sort option is built into Firefox. Bad for some users, while other users (like me) prefer it that way.

Here's a tip: If you add a Separator to your bookmarks listing the Sort Order will be restricted to within or between Separators, which I really like. Separate batches of bookmarks that always stay in the expected order, while other batches can be sorted at user will. Plus that feature helps users who may install an add-on that auto alphabetizes new bookmarks as they are saved. I haven't used that type of add-on for many years, but I did like maybe 10 years or so.

Oh, and I think that Other Bookmarks (formerly known as Unsorted Bookmarks) was originally intended for quick saves of new bookmarks to keep all the new ones in one folder waiting for the user to sort them later in batches.

You need to right-click a folder to sort all items in this folder.
Sorting is done between separators, so you can place all folders at the top and add a separator before the bookmarks.

• https://support.mozilla.org/en-US/kb/sort-bookmarks-quickly-find-ones-you-want

See also:

• https://support.mozilla.org/en-US/kb/bookmark-folders-organize-your-bookmarks