Do you perhaps have muscle memory for the Ctrl+Shift+B shortcut that used to open a large side panel but now just shows a narrow horizontal bar?
I do and I'm certainly annoyed by this redesign, but I discovered the "manage bookmarks" shortcut Ctrl+Shift+O that opens a larger pop-up window with your bookmarks, which so far seems almost as comfortable as the old side panel.
It also lets you search for bookmarks and right-clicking to select "show in folder" in the context menu shows you where in the hierarchy it is. (Though all my bookmarks are in "other bookmarks", so I don't expect to be using this much.)
No, I don't have muscle memory, and in fact you have introduced me to the Ctrl+Shift+B shortcut to show or hide the Bookmarks Toolbar! :-D I won't use it though, because I have it visible and it's not something one typically changes a lot.
With "side panels" I mean what strictly speaking Firefox calls "Sidebar": menu View -> Sidebar -> choose ONE among Bookmarks, History, Synced Tabs, Bookmark search plus 2, or Tree Style Tab.
Why the hell I cannot have e.g. Tree Style Tab AND a Bookmarks sidebars on the left, at the same time? Seems silly to me. Ages ago I worked with Qt and made desktop applications that could have detachable panels (QDockWidget), or their native equivalents such as palettes on Windows, that could be placed anywhere on a main window; but now that we're living in the future it seems we went backwards on what our UIs are able to do.
I do and I'm certainly annoyed by this redesign, but I discovered the "manage bookmarks" shortcut Ctrl+Shift+O that opens a larger pop-up window with your bookmarks, which so far seems almost as comfortable as the old side panel.
It also lets you search for bookmarks and right-clicking to select "show in folder" in the context menu shows you where in the hierarchy it is. (Though all my bookmarks are in "other bookmarks", so I don't expect to be using this much.)