The latest version of Firefox, version 8, is slated to be officially released on November 8th. However, it's actually available now via Mozilla's FTP servers. The biggest change is that Firefox is a little more careful with add-ons, setting them to disabled by default and presenting upgraders a one-time dialog box to manage previously installed add-ons. There's also support for Twitter in the search bar, a preference to load tabs on-demand after a relaunch, and the standard performance and stability fixes.
You can find the download link at Mozilla's FTP site, but a full release (including mirrors for faster downloading) should be arriving on Tuesday — so if you're not in a hurry you can just wait for your browser to offer an auto-update.