There are only three options to sort bookmarks in Firefox. The first is the default way where you add bookmarks and they are placed in order that you added them. The second way is to manually adjust their order, and the third "Sort by Name". You don’t have any other options besides that.
With SortPlaces however, you do:
SortPlaces is probably the best bookmark sorter I’ve ever seen for any web browser. You can sort by almost anything:
You can include or exclude anything you want, and even set up automatic sorting:
SortPlaces is even smart enough to place access points in places where you would actually need them. You can sort from the bottom toolbar, in the bookmark menu and/or in the bookmark manager.
This add-on, put simply, is incredible. I’ve seen nothing else that even comes close, and it definitely qualifies as one of those must-have add-ons if you use bookmarks heavily in the Firefox browser.