Firefox can display bookmarks in 3 places:

• Bookmarks Toolbar (does stay open, but only shows a few items)
• Drop-down menu (does not stay open after you click an item)
• Bookmarks Sidebar (stays open until you close the window)

To open and close the Bookmarks Sidebar, press Ctrl+b (assuming your cursor is not in a text editor that interprets Ctrl+b to mean bold some text). Is that what you're looking for??

• Toggle the Bookmarks sidebar on/off via "View > Sidebar > Bookmarks" or Ctrl+B (Command+B on Mac)
• Toggle the History sidebar on/off via "View > Sidebar > History" or Ctrl+H (Command+H on Mac)

• Press the F10 key or tap the Alt key to bring up the hidden "Menu Bar" temporarily.

• https://support.mozilla.org/kb/how-do-i-use-bookmarks