Sorry, there isn't a feature in Firefox to allow that to be changed. Although there may be an add-on that adds that type of feature to Firefox; but I don't know, never looked for an add-on like that.

If you click the "Star" a 2nd time, an "Edit this Bookmark" dialog will appear, allowing you to move the new bookmark to where you want it. Although that dialog window is rather small and needs a bit of "learning" or experimentation to figure it out.