If the bookmark is on the Bookmarks Toolbar, just right-click on it.

or

Open the Bookmarks Manager; Press the Alt or F10 key to bring up the toolbar, and select Bookmarks. Hot key is <Control> (Mac=<Command>) <Shift> B. Firefox 84+ <Control> (Mac=<Command>) <Shift> O.

Find the bookmark and right-click on it.

Hi Tony, one other note:

If you found suggestions to "right-click" a bookmark but you have a one-button mouse, use Ctrl+click to call up the context menu for the bookmark.