Firefox 54: multi-process gets another content process

The most recent Nightly version of the Firefox browser, Firefox Nightly 54, ships with two content processes instead of just one.
 
Firefox's multi-process architecture still rolls out to Firefox stable versions. That process will still take a couple of release cycles to reach all users of the stable version of the Firefox web browser.
 
Firefox uses a content process for all tabs open in the browser, and a separate process for the browser core.  Separating the core browser from the rest improves stability, and also responsiveness and other metrics of the browser.
 
If a tab crashes, there is less chance that it will take the whole browser with it doing so.
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