As expected, Mozilla has released the first Firefox beta featuring out of process plugins (OOPP), or plugins running on their own process, so if one crashes it won’t take down all your Firefox session. Instead, the plugin is replaced with a dark image notifying the plugin crash, and display a link you can click on to try to reload the plugin.
The feature has been ready for about two months, and in the latest days Mozilla has been ironing stability bugs, and back porting it from the trunk (main development repository), to the Namoroka branch (Firefox 3.6.x).
Right now, it only runs QuickTime, Flash, and Silverlight on their own process, but you can also manually add other plugins via about:config.
For example to have the Adobe Reader plugin running on its own process, create a boolean preference in about:config, name it dom.ipc.plugins.enabled.nppdf32.dll, set it to true, and restart. For Java, the preference must be named dom.ipc.plugins.enabled.npjp2.dll. You just need to know the name of the library (which you get from about:plugins), and create the preference accordingly.
Conversely, you can disable OOPP for specific plugins (even enabled by default ones) by setting their respective preference to false.
Remember, however, that there is a reason for not running all plugins on their own process, so be prepared to turn back if things get unstable.
Also, realize that there is a memory hit when running plugins on their own process. I made a simple test running Firefox with four YouTube videos playing in separate tabs for about one minute. I found Firefox took around 220MB and 240MB (firefox.exe + mozilla-runtime.exe processes) when running Flash running in-process and out of process respectively, or about a 10% overhead. But I guess your mileage could vary significantly depending on the plugin and the actual content. Please feel free to share your results here.
Lorentz is the first outcome of Electrolysis, a major project that also aims to move Firefox user interface, and tabs to their own process for enhanced stability.
Final version of Lorentz is targeted as a minor update for Firefox (3.6.4 most likely) by May.
Check Mozilla’s Firefox Lorentz page to download and test it. Note that while there is a Mac OS X version available it doesn’t come with OOPP yet “because of architectural difference”, according the release notes.