The new Firefox beta also allows you to disable insecure content at will on Web sites that have been secured with HTTPS. In the beta, the feature is only available through about:config.
The Mac version now works with high-definition Retina displays, and all Firefox Beta platforms support W3C touch screen-specific events, as well as MozTouch events.
Other changes include built-in viewing of PDFs, and early support for WebRTC, which eventually will let browsers run P2P apps, perform voice calls, and power video chats without plug-ins. Full notes on what's new in Firefox 18 beta can be read here.