Perhaps the most talked about feature in the new release is the PDF viewer based on HTML5. Firefox users will no longer have to rely on external plugins like the Adobe Reader PDF plugin, to view PDF files. The use of external plugins made browsing slower and at the times the plugins tended not to work properly. External plugins also had vulnerabilities that could be exploited. Users no longer have to worry about that as PDF files can be viewed within the browser.
Other updates in the browser are mostly focused on developer tools for the CSS and bug fixes, probably something that the average user will not fancy much. A complete list of release notes should be available tomorrow at the official launch.