If you have accidentally removed bookmarks then use "Organize > Undo" in the bookmarks manager (Bookmarks > Show All Bookmarks) to get them back.
The Organize button is the first of the three buttons next to the Back and Forward buttons on the toolbar in the Library (Bookmarks Manager).
That only works if you haven't closed Firefox.

Thanks cor- el for your response.

Does that mean then, that there is no way to set up things, to give a warning before deleting boolmarks? That is more what I was looking for.

Thanks, E

No, you can't get a warning before deleting bookmarks.
If you notice too late and already have restarted Firefox then you will have to restore from a daily JSON backup in the bookmarkbackups folder.

• http://kb.mozillazine.org/Backing_up_and_restoring_bookmarks_-_Firefox

Thank you cor-el I will look at the links you sent.

I appreciate your help

E