The toolbar, you mean the personal tool bar on the top?
Sorry, misread qyestion I guess. As others have said it seems that it depends on a number of things, the length of the description, whether or not there is an icon associated with it, your theme, your screen resolution and browser window size.
http://texturizer.net/firefox/extensions/#optimoztweaks
Get that extension, its my favorite. Optimoz tweaks. Makes your bookmarks sidebar autohide so it doesnt take up 1/4 of your browser window. You can see them all that way.
After you get it you have to turn it on, set the sensitivity to about 6 or 7 , seems to make it open better