Have you read this archived thread?

https://support.mozilla.org/en-US/questions/1341634#:~:text=Hi%20Anne%2C%20you%20can%20either%20*%20press%20the%20keyboard%20shortcut%20Ctrl,bookmarks%2C%20history%20and%20synced%20tabs

You can toggle the Bookmarks sidebar via "Ctrl+B".

• https://support.mozilla.org/en-US/kb/use-firefox-sidebar-access-bookmarks-history-synced

I don't believe that any of the answers are satisfactory as I interpret the question as the requester wanting the "bookmarks toolbar" to be relocatable to the left-hand (or right-hand) side, and not to open the "bookmarks sidebar".

I would also like this, a very slim bar (and not something that takes up a sizeable portion of the real-estate) where you can see the icons for your bookmarks, and with an additional behavior to also expand when you hover or show in tooltips-like manner the bookmark name, and as soon as you click, the hover disappears.

I could elaborate more on this if you want.

You can move Bookmarks Toolbar Items from the Bookmarks Toolbar to another toolbar but that's it (other than using the sidebar).