If you notice you lost bookmarks or accidentally deleted bookmark(s) and you haven't closed Firefox yet then you can use "Organize -> Undo" in the bookmarks manager (Bookmarks -> Show All Bookmarks) to undo this action and restore bookmark(s) you deleted accidentally or otherwise lost/misplaced. You may have to use Undo more than once (Firefox keeps a full undo stack of changes to bookmarks for the current session). Otherwise you can consider to restore the bookmarks from a JSON backup in the bookmarkbackups folder. *Bookmarks -> Show All Bookmarks -> Import & Backup -> Restore This will replace all current bookmarks and you lose bookmarks that were added since that backup was created, so you may want to create an HTML backup on beforehand. The name of an automatically created JSON bookmarks backup in the bookmarkbackups folder includes a total item count (folders and separators included) and an hash value to prevent saving the same backup more than once. You also see this count in the Restore menu drop-down list. *bookmarks-YYYY-MM-DD_<item count>_<hash>.jsonlz4. ---- On Mac you only have three icons on the toolbar in the Library and no text to easily identify their purpose. In the Bookmarks Manager (Library) there is a toolbar with the Back and Forward button and three other buttons (Organize, Views, Import & Backup). If you hover a button then you should see a descriptive tooltip text. * first button (cogwheel <img src="https://hg.mozilla.org/releases/mozilla-release/raw-file/tip/toolkit/themes/shared/icons/settings.svg">): Organize (Organize your bookmarks) * second button (<img src="https://hg.mozilla.org/releases/mozilla-release/raw-file/tip/browser/themes/shared/icons/sort.svg">): Views (Change your view) * third button (up/down arrow <img src="https://hg.mozilla.org/releases/mozilla-release/raw-file/tip/browser/themes/shared/icons/import-export.svg">): Import & Backup (Import and backup your bookmarks) https://hg.mozilla.org/releases/mozilla-release/file/tip/toolkit/themes/shared/icons/settings.svg