Encountered something (maybe) similar to this bug. It seems that the "Edit Bookmark", "Add Bookmark" & "Add bookmark folder" panels are opened in background if those context menu options are clicked on a bookmark which is placed withing a bookmark folder or via "Show more bookmarks" menu.
Bug 1705120 Comment 7 Edit History
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Encountered something (maybe) similar to this bug. It seems that the "Edit Bookmark", "Add Bookmark" & "Add bookmark folder" modals are opened in background if those context menu options are clicked on a bookmark which is placed withing a bookmark folder or via "Show more bookmarks" menu.