Electrolysis is the Mozilla project which deals with the out of process plugins and tab handling.
This feature gives the tabs and plugins the ability to run out of process. So, in case of a misbehaving plugin or tab, it can be safely closed without disturbing the whole browsing session.
Out of process plugins allow the browser to run the plugins in a separate sandboxed area.
This change has appeared on the recent developer preview build released by Firefox. The Alpha 2 release of Firefox 4.0 is still named Firefox 3.7 though.
Apart from the out of process plugin, the new features in Firefox 4.0 Alpha 2 are,
- Link history lookup removed from main thread and made asynchronous.
- Loading HTML5 spec no longer causes long pauses.
- Layout performance improvements (DOM access time, color management, text area, etc.).
- Many new features for developers.
The layout improvement means faster rendering on web pages and the support for recursion and better string handling means more RAM consumption and faster JS rendering.
The out of process plugin is a feature present in Google Chrome for a long time now. Chrome add-ons are catching up. Chrome definitely delivers pages faster and in the midst of all this, Firefox is going to lose out in the browser race if it does not do something awesome soon.