Sounds that you are using the wrong toolbar button.

Firefox 4+ versions have two bookmark buttons with a star in the Customize window.
One star button has a drop marker that open a Bookmark menu.
The other star button without the drop marker opens the bookmarks in the sidebar.

You can drag the Bookmarks menu button with the drop marker in the Customize window from the toolbar palette on a toolbar (e.g. Navigation Toolbar or Tab Bar or to the left side of the Bookmarks Menu Items).

• https://support.mozilla.org/kb/Back+and+forward+or+other+toolbar+items+are+missing

There are two kinds of bookmark buttons. The one with the menu is the regular, default toolbar item. It has a star in it AND a little down arrow. If you right-click on that button (or a blank part of the toolbar) and choose customize, you can get rid of that button and replace it with the other bookmarks button that just has a star in it (no little down arrow). That other bookmarks button opens the sidebar.

For more info about customizing button and toolbars see, Customize Firefox controls, buttons and toolbars .

That's very interesting. I have never knowingly changed the bookmark button from the one that was set up many years ago. Looking at the custom menu toolbox, there is not another bookmark button in there.

I might try resetting the default toolbars or make a new profile to see if this helps.

In your case you are looking for the button without the drop marker to open the side bar (Ctrl+B).

You will probably find the button with the drop marker at the end of the Bookmarks Toolbar though it only will show there if the menu bar is hidden and you have the orange Firefox button visible.

See also:

• http://kb.mozillazine.org/Corrupt_localstore.rdf
• https://support.mozilla.org/kb/Toolbar+keeps+resetting

Cor-el: Yes, you're right. I have both the bookmark toolbar and the navigation toolbar hidden to save screen space. Restoring those revealed the "proper" bookmark button, which I have put back where I can see it. Many thanks for your help.