Reddit - over the weekend, Reddit launched and tweaked many of its features, most noticeably the layout of subreddits which are now displayed in a thin bar on the top of the page. Other features include a slightly different design for various subreddits and different positioning of the search form.
Furthermore, toolbar lovers will be happy to know that there's a Firefox extension called Socialite which brings many of Reddit's features into the browser. Click on a Reddit link, and the toolbar will show up; you can now vote, save, and hide links. If you like, you can open the toolbar manually by clicking on the little Reddit icon in the Firefox address bar; now, you can use it to submit links to Reddit as you browse the Web.
Most other popular social bookmarking sites have some version of a Firefox toolbar, too. Here's a quick reminder:
Digg - this toolbar gives you access to main features of Digg like submitting new stories and checking out the "best of" selection of stories. It also adds a Google-powered search box to the mix.
Delicious - this plugin is more than just a toolbar; it basically replaces (it's reversible, don't worry) your Firefox bookmarking system with that of Delicious. A must have for frequent users of this social bookmarking site.
StumbleUpon - If there's one social bookmarking toolbar you need to install, get this one. StumbleUpon's simple concept of stumbling onto popular websites works even better if you do it through a toolbar. If you don't want to clutter your Firefox, though, you can use the latest StumbleUpon feature: the Web toolbar.
Firevine: This toolbar is no longer a toolbar; the developer of the plugin decided it's better to integrate everything directly into Firefox. It features an automatically updated watchlist, a seed status checker, context menu and more.