Click the arrow at the far right (outside) of the folder field (i.e. not the arrow in the folder field, but the one further to the right) in the "Edit This Bookmark" window to access the complete folder list. The full folder list also opens if you click the drop marker in the Folder field and click the "Choose..." item. The full folder window has a button to create a "New Folder" (look for a button with "New Folder" or a "+" under the folder list). If you do not see all folders in the full folder list then it is possible that folders are collapsed. If that is the case then you need to expand folders to see other folders that it contains. You can look for a faint arrow or twisty at the far left and click this icon to expand (open) the folder and show its content.

There is a pref that defaults to 7 to set the number of entries to show in the list of recently used folders (first Down arrow in the folder line).

• about:config => browser.bookmarks.editDialog.maxRecentFolders (7)

• https://support.mozilla.org/en-US/kb/about-config-editor-firefox

I don't have a clue where the right hand arrow is that brings up edit this bookmark. Maybe you can start me off with telling me if I need to open something other than the sidebar where I have my bookmarks pinned. I searched in the applications menu and still don't see this right hand arrow related to the folders in my bookmark section.