Currently, sorting bookmarks in Firefox seems to be limited and not very intuitive. There is an extension that makes the job of sorting your bookmarks more flexible and automatic.
SortPlaces allows you to sort your bookmarks by different criteria and automatically as you add bookmarks.
Install the SortPlaces extension from: HERE
Firefox will restart after installation, preserving any open tabs.
To set up the options for SortPlaces, select Sort Bookmarks from the Bookmarks menu and select Options from the submenu.
The SortPlaces dialog box displays. You can set different sort options for the Menu, Toolbar and Unfiled bookmarks separately, and for each you can set two levels of sorting.
On each of the three tabs, select the criteria by which you want to sort the bookmarks on both levels (the Sort items by tab and the Then items by tab). Select Unsorted as the Sort by option to preserve the order your bookmarks.
Bookmarks, folders etc. are normally sorted in increasing alphabetical or numerical order depending on the option chosen. Click the Reverse order check box to change this.
If you choose Name or Description from the Sort by drop-down list, your bookmarks are normally sorted in a case sensitive way, e.g. ‘a’ comes before ‘A’. Click the Case insensitive check box to completely ignore this when sorting (i.e. ‘a’ == ‘A’).
NOTE: The Case insensitive option is only available for the first level of sorting criteria.
The Folder ordering box allows you to specify how you want to group and order the four bookmark types available in Firefox. The lower numbers entered indicate a higher position in the order.
For example if you wish folders to always appear before queries, and queries before bookmarks, with livemarks grouped together at the bottom, then set Folders to ‘1′, Queries to ‘2′, Bookmarks to ‘3′ and Livemarks to ‘4′, as pictured in the following image.
If you wish two or more items to be treated equally and not grouped together, then set the order of them to be the same, e.g., set both Bookmarks and Livemarks to ‘3′.
To have your bookmarks automatically sorted as you add them, click the Options tab on the SortPlaces dialog box and click the Sort automatically check box.
To specify a time delay before the current web page is bookmarked, enter a number in the Delay edit box. This value is in seconds.
NOTE: The Delay option prevents unnecessary sorting when you’re making a lot of changes to your Bookmarks list. It also prevents the automatic sorting from interfering with certain bookmark operations that can take a while to complete (e.g., when adding a new folder, the folder’s name may be committed or cancelled by the automatic sorting before you’ve finished typing it in).
The Display options box allows you to specify where the SortPlaces option is available within Firefox.
For more help on using this extension, see HERE
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SortPlaces allows you to sort your bookmarks by different criteria and automatically as you add bookmarks.
Install the SortPlaces extension from: HERE
Firefox will restart after installation, preserving any open tabs.
To set up the options for SortPlaces, select Sort Bookmarks from the Bookmarks menu and select Options from the submenu.

The SortPlaces dialog box displays. You can set different sort options for the Menu, Toolbar and Unfiled bookmarks separately, and for each you can set two levels of sorting.
On each of the three tabs, select the criteria by which you want to sort the bookmarks on both levels (the Sort items by tab and the Then items by tab). Select Unsorted as the Sort by option to preserve the order your bookmarks.

Bookmarks, folders etc. are normally sorted in increasing alphabetical or numerical order depending on the option chosen. Click the Reverse order check box to change this.

If you choose Name or Description from the Sort by drop-down list, your bookmarks are normally sorted in a case sensitive way, e.g. ‘a’ comes before ‘A’. Click the Case insensitive check box to completely ignore this when sorting (i.e. ‘a’ == ‘A’).
NOTE: The Case insensitive option is only available for the first level of sorting criteria.
The Folder ordering box allows you to specify how you want to group and order the four bookmark types available in Firefox. The lower numbers entered indicate a higher position in the order.
For example if you wish folders to always appear before queries, and queries before bookmarks, with livemarks grouped together at the bottom, then set Folders to ‘1′, Queries to ‘2′, Bookmarks to ‘3′ and Livemarks to ‘4′, as pictured in the following image.

If you wish two or more items to be treated equally and not grouped together, then set the order of them to be the same, e.g., set both Bookmarks and Livemarks to ‘3′.
To have your bookmarks automatically sorted as you add them, click the Options tab on the SortPlaces dialog box and click the Sort automatically check box.

To specify a time delay before the current web page is bookmarked, enter a number in the Delay edit box. This value is in seconds.
NOTE: The Delay option prevents unnecessary sorting when you’re making a lot of changes to your Bookmarks list. It also prevents the automatic sorting from interfering with certain bookmark operations that can take a while to complete (e.g., when adding a new folder, the folder’s name may be committed or cancelled by the automatic sorting before you’ve finished typing it in).
The Display options box allows you to specify where the SortPlaces option is available within Firefox.
For more help on using this extension, see HERE
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