hello edanddarlene,

There is some extra features when it comes to bookmarks in FF. They can be accessed by going to menu bar and selecting bookmarks and then show all.

Or a quick method is by pressing the key combinations of control+shift+O, the bookmark section will open up.

From there you can delete them easier.

If you want to select a group of them simply click on one bookmark, then hold the shift key down and then click the down arrow key. This will select many at once and then you can press the delete key.

Selecting multiple bookmark items works the same as in other cases. In the Bookmarks Manager (Library) you can toggle individual items by holding the Ctrl key.

Note that best is not to select too many items (more than a few hundred) at the same time as deleting is done in small chunks and may take quite some time to finish.