Regarding Firefox 57 (Nov 2017)
ManageFolders will not work with Firefox 57 and beyond. FF-57 disables the ability to change the general UI of FF itself, which ManageFolders requires to add the menu-item. At this time, Mozilla has no plan to re-enable the level of UI control ManageFolders needs.
If you liked this extension, please VOTE for this issue in Bugzilla : https://bugzilla.mozilla.org/show_bug.cgi?id=1406282
You can vote in the "Details" section after signing in (you can sign in via github!)
Firefox plug-in which places a "Manage Folder" item on the context menu of bookmark folders. This opens the "Places Organizer" with the specific folder expanded, ready for editing. This feature, originally in Firefox 1.0 but removed in 1.5, makes it easy to organize a specific bookmark folder when you realize it needs to be re-organized.