If the Firefox bookmarks toolbar isn't doing the job, take a look at Samfind Bookmarks Bar. This free add-on provides access to many more sites and services in the same amount of space as the regular bookmarks toolbar. It's a capable tool, but not quite as straightforward to use as the regular toolbar.
Once you download Samfind, you'll see a new toolbar below the bookmarks toolbar--one chock full of options. On the left, you get icons that allow quick access to bookmarks and social networking, such as del.icio.us, Facebook and Reddit for marking or sharing a site, along with a button for quickly e-mailing the link to friends. Buttons for recommendation sites (such as Digg) display the number of times someone else has recommended the page you're on.
Then on the right side, you'll see a list of topic names such as search, news, videos or blogs. Clicking any of those topics expands it to show a pre-populated list of sites in that topic, such as Google news, Digg, CNN, BBC News and other sites under a news topic.
Most topics will by default display a search box in which you can enter a term and quickly search one of the sites. The maps topic allows for typing in a start and end location to get directions from Google Maps or Yahoo! Maps. If a site offers an RSS feed, you can check its latest posts using a drop-down next to its button.
It's a cinch to go into the add-on's options and click a button to pull in all your current Bookmarks toolbar links into a new, integrated 'my bookmarks' topic--but if you add a new site to the bookmark toolbar afterwards it won't automatically make it into the 'my bookmarks' topic. And clicking the button again will give you a bunch of samfind duplicates.
To add new pages to a topic, your easiest option by far is to click on the browser tab with that page open and drag it to the topic. It's not an entirely intuitive option, but it's simple once you know to do it. You can also remove and re-order the displayed topics or sites, and configure how everything looks on the toolbar.
It's a shame Samfind doesn't integrate with the regular Firefox bookmarks system, which would make it easier and more intuitive to use. But even without that integration, it's a good way to pack many more sites into your bookmarks toolbar.