Open Firefox
Click the Library icon or press Ctrl+Shift+O
Select Bookmarks
Open the folder containing the bookmark
Drag the bookmark to the desired folder or position
Release the mouse button to drop it
To move multiple bookmarks, select them and drag them together
To move a bookmark from the bookmarks toolbar, drag it to another folder or location
To move bookmarks using the menu, right-click the bookmark and choose Cut
Open the destination folder
Right-click inside the folder and choose Paste