I'm aware of two older extensions that say they can keep your bookmarks sorted in reverse chronological order (I have not tested myself):

• https://addons.mozilla.org/firefox/addon/sort-bookmarks-webext/
• https://addons.mozilla.org/firefox/addon/auto-sort-bookmarks/

Thank you, but you may want to read my message until its end - it says I already know about sorting, but that would negate any custom ordering done before. I just need something that puts the new bookmark on top of the list - when no sorting is active (which is default state).

Whoops, then please do not try those two extensions.

The only other one that comes to mind is a tool for people who are particular about what folders they save in because they like to access them directly from the menu/toolbar. Instead of adding a bookmark and then choosing a folder from a list, you first go to the folder, right-click and add the bookmark there.

https://addons.mozilla.org/firefox/addon/bookmark-tab-here/

You can also drag the tab or padlock icon to the top of a bookmarks folder to create the bookmark in a fixed position.

• https://support.mozilla.org/en-US/kb/use-firefox-sidebar-access-bookmarks-history-synced

You can drag the Bookmarks Menu button that shows the bookmarks in a drop-down list and drag the Library button that gives access to recent bookmarks and history from the Customize palette to the Navigation Toolbar. The Bookmarks Menu button has a "View bookmarks sidebar" menu item.

See "How do I add the Bookmarks Menu button to the toolbar?"

• https://support.mozilla.org/en-US/kb/bookmarks-firefox
• https://support.mozilla.org/en-US/kb/use-firefox-sidebar-access-bookmarks-history-synced

.

@jscher2000: the Bookmark Tab Here extension can drop the bookmark at the top of the folder, but requires for that bookmark to be already opened in a tab. Not quite what I'm looking for, but a step in the right direction.

@cor-el: the Bookmarks Menu button Bookmark Menu icon (star on tray) opens the Bookmarks sidebar (it can also be opened with Ctrl+B on my Manjaro Linux). I'm not using it because it requires a click for each level of the dropdown, while the bookmarks toolbar opens folders on hover. Nevertheless, I'm doing what you describe with the bookmarks toolbar. I'm looking for a way to have the bookmarks created in or dropped on a closed folder positioned at the top of the unsorted list.

BTW, I realized my original post borked the link, so here are:

• the Mozilla Support thread: https://support.mozilla.org/en-US/questions/886289
• the extinct addon: https://web.archive.org/web/20180412201830/https://addons.mozilla.org/en-US/firefox/addon/add-bookmark-here-2/

Okay, that was helpful for context. Try this:

• Expand the bookmark folder where you would like "Add Bookmarks Here"
• Right-click the top item in the folder, then click Add Bookmark
• Enter details and save

The new bookmark should be added above whatever item you right-clicked.