To use this feature, first open your History list by choosing History --> Show All History or by pressing Ctrl-Shift-H. Then right-click the site you want to remove, and from the menu that appears, select Forget about This Site.

You can also remove all of your history and other data related to your browsing session from the last few hours or last day. Select Tools --> Clear Recent History, or press Ctrl-Shift-Del. From the drop-down list on the page that appears, choose either the last hour, the last two hours, the last four hours, today, or everything.

You can also fine-tune what to clear by clicking the Details button; it lets you determine what data to remove -- browsing and download history, forms and search history, cookies, cache, logins, etc.

The new version of Firefox has some nice interface tweaks as well. Primary among them is the ability to re-open tabs or windows that you've previously closed -- functionality that was previously available only through add-ons.