Mozilla today made its Mozilla Developer Preview available for anyone who wants to play around with it. This marks the second pre-release version of the Gecko 1.9.3 platform.
The biggest news with this latest release is the out-of-process plugin support. Plugins, such as Flash and Silverlight, now run in a separate process similar to Chrome, so if a plugin goes belly up, it won't crash the browser along with it. In addition, unresponsive plugins are automatically restarted in the developer preview.
See here for a full list of features and download information.