"Views -> Sort" in the Library does what its name says and is only for viewing purposes and shows a sorted list similar to clicking a column on the header bar. Once you close the Bookmarks Manager (Library) window you lose this sorting feature as this choice isn't persistent. If you want to sort bookmarks then you need to right-click a folder and use "Sort By Name" to sort this folder. You can't right-click individual bookmarks to sort them, only folders can be sorted this way. You can sort the bookmarks manually and drag bookmarks in the desired order. If dragging doesn't work properly then use Cut and Paste instead. *https://support.mozilla.org/en-US/kb/sort-bookmarks-quickly-find-ones-you-want