You can use the Roomy Bookmarks Toolbar add-on to hide the text - https://addons.mozilla.org/firefox/addon/roomy-bookmarks-toolbar/

thanks TonyE thats exactly what I needed. Yay for you. Karen

You can do this with individual bookmarks. Right click on the bookmark and in Properties you can abbreviate the name as much as you wish down to nothing.

To save space you can also create folders of related bookmarks on the toolbar where you can open any you wish up to "Open All in Tabs".