Windows/Mac/Linux: Mozilla's second Developer Preview of Firefox 4.0's framework and back-end highlights a feature we'd heard was coming: separate processes for plug-ins. That means if (when) Flash or another plug-in crashes, there's a good chance your browser won't go with it.

This second alpha of Firefox 3.7—which is, confusingly, what will actually be released as 4.0—adds some performance improvements and HTML5 efficiencies, but the main new thing is the "out-of-process" plug-ins. Contained, stand-alone processes for each tab and add-on are likely in Firefox's future, but starting off with the most likely crash candidates is a good start.

Those interested in kicking the tires really hard on Flash crashes and reporting back to Mozilla should give it a go, as should anyone developing extensions or testing site compatibility. Everybody else looking to test it should try a more contained method.

This Firefox developer preview is a free download, available for Windows, Mac, and Linux systems.